Guidance for Industry | M7(R2) Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals To Limit Potential Carcinogenic Risk

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M7(R2) Assessment and
Control of DNA Reactive
(Mutagenic) 	Impurities in
Pharmaceuticals to Limit
Potential 	Carcinogenic Risk
Guidance for Industry
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Drug Evaluation and Research (CDER)
Center for Biologics Evaluation and Research (CBER)
July 2023
ICH-Multidisciplinary

Contains Nonbinding Recommendations
M7(R2) Assessment and
Control of DNA Reactive
(Mutagenic) 	Impurities in
Pharmaceuticals to Limit
Potential 	Carcinogenic Risk
Guidance for Industry
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https://www.fda.gov/vaccines-blood-biologics/guidance-compliance-regulatory-information-biologics/biologics-guidances
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Drug Evaluation and Research (CDER)
Center for Biologics Evaluation and Research (CBER)
July 2023
ICH-Multidisciplinary

Contains Nonbinding Recommendations
FOREWORD
The International Council for Harmonisation of Technical Requirements for Pharmaceuticals
for Human Use (ICH) has the mission of achieving greater regulatory harmonization
worldwide to ensure that safe, effective, and high-quality medicines are developed,
registered, and maintained in the most resource-efficient manner. By harmonizing the
regulatory expectations in regions around the world, ICH guidelines have substantially
reduced duplicative clinical studies, prevented unnecessary animal studies, standardized
safety reporting and marketing application submissions, and contributed to many other
improvements in the quality of global drug development and manufacturing and the products
available to patients.
ICH is a consensus-driven process that involves technical experts from regulatory authorities
and industry parties in detailed technical and science-based harmonization work that results
in the development of ICH guidelines. 	The commitment to consistent adoption of these
consensus-based guidelines by regulators around the globe is critical to realizing the benefits
of safe, effective, and high-quality medicines for patients as well as for industry. 	As a
Founding Regulatory Member of ICH, the Food and Drug Administration (FDA) plays a
major role in the development of each of the ICH guidelines, which FDA then adopts and
issues as guidance to industry.

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TABLE OF CONTENTS
I. 	INTRODUCTION (1) .................................................................................................. 1
II. 	SCOPE OF GUIDANCE (2) ....................................................................................... 2
III. 	GENERAL PRINCIPLES (3) ..................................................................................... 2
IV. 	CONSIDERATIONS FOR MARKETED PRODUCTS (4) .................................... 4
A. 	Postapproval Changes to the Drug Substance Chemistry, Manufacturing, and
Controls (4.1) ............................................................................................................................ 4
B. 	Postapproval Changes to the Drug Product Chemistry, Manufacturing, and
Controls (4.2) ............................................................................................................................ 4
C. 	Changes to the Clinical Use of Marketed Products (4.3)...................................................... 5
D. 	Other Considerations for Marketed Products (4.4) .............................................................. 5
V. 	DRUG SUBSTANCE AND DRUG PRODUCT IMPURITY ASSESSMENT (5) . 5
A. 	Synthetic Impurities (5.1) ........................................................................................................ 6
B. 	Degradation Products (5.2) ..................................................................................................... 6
C. 	Considerations for Clinical Development (5.3) ..................................................................... 7
VI. 	HAZARD ASSESSMENT ELEMENTS (6) .............................................................. 7
VII. 	RISK CHARACTERIZATION (7) ............................................................................ 9
A. 	TTC-based Acceptable Intakes (7.1) ...................................................................................... 9
B. 	Acceptable Intakes Based on Compound-Specific Risk Assessments (7.2) ........................ 9
1. Mutagenic Impurities With Positive Carcinogenicity Data (Class 1 in Table 1) (7.2.1) ........... 9
2. Mutagenic Impurities with Evidence for a Practical Threshold (7.2.2) .................................... 9
C. 	Acceptable Intakes in Relation to LTL Exposure (7.3) ...................................................... 10
1. Clinical Development (7.3.1) ................................................................................................... 10
2. Marketed Products (7.3.2) ....................................................................................................... 11
D. 	Acceptable Intakes for Multiple Mutagenic Impurities (7.4)............................................. 11
E. 	Exceptions and Flexibility in Approaches (7.5) ................................................................... 11
VIII. 	CONTROL (8)............................................................................................................ 12
A. 	Control of Process-Related Impurities (8.1) ........................................................................ 13
B. 	Considerations for Control Approaches (8.2) ..................................................................... 14
C. 	Considerations for Periodic Testing (8.3) ............................................................................ 15
D. 	Control of Degradation Products (8.4)................................................................................. 15
E. 	Lifecycle Management (8.5) .................................................................................................. 15
F. 	Considerations for Clinical Development (8.6) ................................................................... 16
IX. 	DOCUMENTATION (9) ........................................................................................... 17
A. 	Clinical Trial Applications (9.1) ........................................................................................... 17
B. 	Common Technical Document (Marketing Application) (9.2) .......................................... 17
NOTES .................................................................................................................................... 18

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GLOSSARY............................................................................................................................ 23
REFERENCES....................................................................................................................... 25
APPENDIX 1: SCOPE SCENARIOS FOR APPLICATION OF THE ICH M7(R2)
GUIDANCE ............................................................................................................................ 27
APPENDIX 2: CASE EXAMPLES TO ILLUSTRATE POTENTIAL CONTROL
APPROACHES ...................................................................................................................... 29
APPENDIX 3: LIST OF COMPOUNDS IN ICH M7(R2) ADDENDUM:
ACCEPTABLE INTAKES OR PERMISSIBLE DAILY EXPOSURES ......................... 31

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M7(R2) Assessment and Control
of DNA Reactive (Mutagenic) Impurities
in Pharmaceuticals to Limit Potential Carcinogenic Risk
Guidance for Industry1
This guidance represents the current thinking of the Food and Drug Administration (FDA or Agency)
on this topic. It does not establish any rights for any person and is not binding on FDA or the public.
You can use an alternative approach if it satisfies the requirements of the applicable statutes and
regulations. To discuss an alternative approach, contact the FDA office responsible for this guidance
as listed on the title page.
I. 	INTRODUCTION (1)2
The synthesis of drug substances involves the use of reactive chemicals, reagents, solvents,
catalysts, and other processing aids. As a result of chemical synthesis or subsequent
degradation, impurities reside in all drug substances and associated drug products. Although
the International Council for Harmonisation (ICH) guidances for industry Q3A Impurities in
New Drug Substances (Revision 2) (ICH Q3A) (June 2008) and Q3B(R2) Impurities in New
Drug Products (ICH Q3B(R2)) (August 2006) (Reference (Ref.) 1, 2) provide guidance for
qualification and control for the majority of the impurities,3 limited guidance is provided for
those impurities that are DNA reactive. The purpose of this guidance is to provide a practical
framework that is applicable to the identification, categorization, qualification, and control of
these mutagenic impurities to limit potential carcinogenic risk. This guidance is intended to
complement ICH Q3A, ICH Q3B(R2) (Note 1), and the ICH guidance for industry M3(R2)
Nonclinical Safety Studies for the Conduct of Human Clinical Trials and Marketing
Authorizations for Pharmaceuticals (January 2010) (Ref. 3).
This guidance emphasizes considerations of both safety and quality risk management in
establishing levels of mutagenic impurities that are expected to pose negligible carcinogenic
risk. It outlines recommendations for assessment and control of mutagenic impurities that
reside or are reasonably expected to reside in final drug substance or product, taking into
consideration the intended conditions of human use.
In general, FDA’s guidance documents do not establish legally enforceable responsibilities.
Instead, guidances describe the Agency’s current thinking on a topic and should be viewed
only as recommendations, unless specific regulatory or statutory requirements are cited. The
1 This guidance was developed within the Expert Working Group (Multidisciplinary) of the International
Council for Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use
(ICH) and has been subject to consultation by the regulatory parties, in accordance with the ICH process. This
document has been endorsed by the ICH Assembly at Step 4 of the ICH process, April 2023. At Step 4 of the
process, the final draft is recommended for adoption to the regulatory bodies of the ICH regions.
2 The numbers in parentheses reflect the organizational breakdown of the document endorsed by the ICH
Assembly at Step 4 of the ICH process, April 2023.
3 We update guidances periodically. To make sure you have the most recent version of a guidance, check the
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.

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use of the word should in Agency guidances means that something is suggested or
recommended, but not required.
II. 	SCOPE OF GUIDANCE (2)
This document is intended to provide guidance for new drug substances and new drug
products during their clinical development and subsequent applications for marketing. It also
applies to postapproval submissions of marketed products, and to new marketing applications
for products with a drug substance that is present in a previously approved product, in both
cases only where:
• 	Changes to the drug substance synthesis result in new impurities or increased
acceptance criteria for existing impurities
• 	Changes in the formulation, composition, or manufacturing process result in new
degradation products or increased acceptance criteria for existing degradation
products
• 	Changes in indication or dosing regimen are made, which significantly affect the
acceptable cancer risk level
Assessment of the mutagenic potential of impurities as described in this guidance is not
intended for the following types of drug substances and drug products:
biological/biotechnological, peptide, oligonucleotide, radiopharmaceutical, fermentation
products, herbal products, and crude products of animal or plant origin.
This guidance does not apply to drug substances and drug products intended for advanced
cancer indications as defined in the scope of the ICH guidance for industry S9 Nonclinical
Evaluation for Anticancer Pharmaceuticals (March 2010) (Ref. 4). Additionally, there may
be some cases where a drug substance intended for other indications is itself genotoxic at
therapeutic concentrations and may be expected to be associated with an increased cancer
risk. Exposure to a mutagenic impurity in these cases would not significantly add to the
cancer risk of the drug substance. Therefore, impurities could be controlled at acceptable
levels for nonmutagenic impurities.
Assessment of the mutagenic potential of impurities as described in this guidance is not
intended for excipients used in existing marketed products, flavoring agents, colorants, and
perfumes. Application of this guidance to leachables associated with drug product packaging
is not intended, but the safety risk assessment principles outlined in this guidance for limiting
potential carcinogenic risk can be used if warranted. The safety risk assessment principles of
this guidance can be used if warranted for impurities in excipients that are used for the first
time in a drug product and are chemically synthesized.
III. 	GENERAL PRINCIPLES (3)
The focus of this guidance is on DNA-reactive substances that have a potential to directly
cause DNA damage when present at low levels leading to mutations and, therefore,
potentially causing cancer. This type of mutagenic carcinogen is usually detected in a

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bacterial reverse mutation (mutagenicity) assay. Other types of genotoxicants that are
nonmutagenic typically have threshold mechanisms and usually do not pose carcinogenic risk
in humans at the level ordinarily present as impurities. Therefore, to limit a possible human
cancer risk associated with the exposure to potentially mutagenic impurities, the bacterial
mutagenicity assay is used to assess the mutagenic potential and the need for controls.
Structure-based assessments are useful for predicting bacterial mutagenicity outcomes based
upon the established knowledge. There are a variety of approaches to conduct this evaluation
including a review of the available literature and/or computational toxicology assessment.
A threshold of toxicological concern (TTC) concept was developed to define an acceptable
intake for any unstudied chemical that poses a negligible risk of carcinogenicity or other toxic
effects. The methods upon which the TTC is based are generally considered to be very
conservative because they involve a simple linear extrapolation from the dose giving a 50
percent tumor incidence (TD50 ) to a 1 in 106 incidence, using TD50 data for the most sensitive
species and most sensitive site of tumor induction. For application of a TTC in the assessment
of acceptable limits of mutagenic impurities in drug substances and drug products, a value of
1.5 micrograms (μg)/day corresponding to a theoretical 10-5 (1 in 100,000) excess lifetime
risk of cancer can be justified. Some structural groups were identified to be of such high
potency that intakes even below the TTC would theoretically be associated with a potential
for a significant carcinogenic risk. This group of high-potency mutagenic carcinogens
referred to as the cohort of concern comprises aflatoxin-like-, N-nitroso-, and alkyl-azoxy
compounds.
During clinical development, it is expected that control strategies and approaches will be less
developed in earlier phases where overall development experience is limited. This guidance
bases acceptable intakes for mutagenic impurities on established risk assessment strategies.
Acceptable risk during the early development phase is set at a theoretically calculated level of
approximately 1 additional cancer per 1 million. For later stages in development and for
marketed products, acceptable increased cancer risk is set at a theoretically calculated level of
approximately 1 in 100,000. These risk levels represent a small theoretical increase in risk
when compared to human overall lifetime incidence of developing any type of cancer, which
is greater than 1 in 3. It is noted that established cancer risk assessments are based on lifetime
exposures. Less-than-lifetime (LTL) exposures during both development and marketing can
have higher acceptable intakes of impurities and still maintain comparable risk levels. The
use of a numerical cancer risk value (1 in 100,000) and its translation into risk-based doses
(TTC) is a highly hypothetical concept that should not be regarded as a realistic indication of
the actual risk. Nevertheless, the TTC concept provides an estimate of safe exposures for any
mutagenic compound. However, exceeding the TTC is not necessarily associated with an
increased cancer risk given the conservative assumptions employed in the derivation of the
TTC value. The most likely increase in cancer incidence is actually much less than 1 in
100,000. In addition, in cases where a mutagenic compound is a noncarcinogen in a rodent
bioassay, there would be no predicted increase in cancer risk. Based on all the above
considerations, any exposure to an impurity that is later identified as a mutagen is not
necessarily associated with an increased cancer risk for subjects already exposed to the
impurity. A risk assessment would determine whether any further actions would be taken.
Where a potential risk has been identified for an impurity, an appropriate control strategy
leveraging process understanding and/or analytical controls should be developed to ensure
that the mutagenic impurity is at or below the acceptable cancer risk level.

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There may be cases when an impurity is also a metabolite of the drug substance. In such
cases, the risk assessment that addresses mutagenicity of the metabolite can qualify the
impurity.
IV. 	CONSIDERATIONS FOR MARKETED PRODUCTS (4)
This guidance is not intended to be applied retrospectively (i.e., to products marketed before
adoption of this guidance). However, some types of postapproval changes warrant a
reassessment of safety relative to mutagenic impurities. This section applies to these
postapproval changes for products marketed before, or after, the adoption of this guidance.
Section VIII.E, Lifecycle Management, (8.5) contains additional recommendations for
products marketed after adoption of this guidance.
A. 	Postapproval Changes to the Drug Substance Chemistry, Manufacturing,
and Controls (4.1)
Postapproval submissions involving the drug substance chemistry, manufacturing, and
controls should include an evaluation of the potential risk impact associated with mutagenic
impurities from changes to the route of synthesis, reagents, solvents, or process conditions
after the starting material. Specifically, changes should be evaluated to determine if the
changes result in any new mutagenic impurities or higher acceptance criteria for existing
mutagenic impurities. Reevaluation of impurities not impacted by changes is not
recommended. For example, when only a portion of the manufacturing process is changed,
the assessment of risk from mutagenic impurities should be limited to whether any new
mutagenic impurities result from the change, whether any mutagenic impurities formed
during the affected step are increased, and whether any known mutagenic impurities from
upstream steps are increased. Regulatory submissions associated with such changes should
describe the assessment as outlined in section IX.B (9.2). Changing the site of manufacture of
a drug substance, intermediates, or starting materials or changing raw materials supplier will
not require a reassessment of mutagenic impurity risk.
When a new drug substance supplier is proposed, evidence that the drug substance produced
by this supplier using the same route of synthesis as an existing drug product marketed in the
assessor’s region is considered to be sufficient evidence of acceptable benefit-risk regarding
mutagenic impurities, and an assessment per this guidance is not required. If this is not the
case, then an assessment per this guidance is expected.
B. 	Postapproval Changes to the Drug Product Chemistry, Manufacturing,
and Controls (4.2)
Postapproval submissions involving the drug product (e.g., change in composition,
manufacturing process, dosage form) should include an evaluation of the potential risk
associated with any new mutagenic degradation products or higher acceptance criteria for
existing mutagenic degradation products. If appropriate, the regulatory submission would
include an updated control strategy. Reevaluation of the drug substance associated with the
drug products is not recommended or expected provided there are no changes to the drug
substance. Changing the site of manufacture of a drug product will not require a reassessment
of mutagenic impurity risk.

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C. 	Changes to the Clinical Use of Marketed Products (4.3)
Changes to the clinical use of marketed products that can warrant a reevaluation of the
mutagenic impurity limits include a significant increase in clinical dose, an increase in
duration of use (in particular when a mutagenic impurity was controlled above the lifetime
acceptable intake for a previous indication that may no longer be appropriate for the longer
treatment duration associated with the new indication), or for a change in indication from a
serious or life-threatening condition where higher acceptable intakes were justified (section
VII.E (7.5)) to an indication for a less serious condition where the existing impurity
acceptable intakes may no longer be appropriate. Changes to the clinical use of marketed
products associated with new routes of administration or expansion into subject populations
that include pregnant individuals and/or pediatric subjects will not warrant a reevaluation,
assuming no increases in daily dose or duration of treatment.
D. 	Other Considerations for Marketed Products (4.4)
Application of this guidance may be warranted to marketed products if there is specific cause
for concern. The existence of impurity structural alerts alone is considered insufficient to
trigger follow-up measures, unless it is a structure in the cohort of concern (section III (3)).
However, a specific cause for concern would be new relevant impurity hazard data (classified
as Class 1 or 2, section VI (6)) generated after the overall control strategy and specifications
for market authorization were established. This new relevant impurity hazard data should be
derived from high-quality scientific studies consistent with relevant regulatory testing
guidelines, with data records or reports readily available. Similarly, a newly discovered
impurity that is a known Class 1 or Class 2 mutagen that is present in a marketed product
could also be a cause for concern. In both of these cases when the applicant becomes aware
of this new information, an evaluation per this guidance should be conducted.
V. 	DRUG SUBSTANCE AND DRUG PRODUCT IMPURITY ASSESSMENT (5)
Actual and potential impurities that are likely to arise during the synthesis and storage of a
new drug substance and during manufacturing and storage of a new drug product should be
assessed.
The impurity assessment is a two-stage process:
• 	Actual impurities that have been identified should be considered for their mutagenic
potential.
• 	An assessment of potential impurities likely to be present in the final drug substance
is carried out to determine if further evaluation of their mutagenic potential is
recommended.
The steps as applied to synthetic impurities and degradation products are described in
sections V.A (5.1) and V.B (5.2), respectively.

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A. 	Synthetic Impurities (5.1)
Actual impurities include those observed in the drug substance above the ICH Q3A reporting
thresholds. Identification of actual impurities is expected when the levels exceed the
identification thresholds outlined by ICH Q3A. It is acknowledged that some impurities
below the identification threshold may also have been identified.
Potential impurities in the drug substance can include starting materials, reagents, and
intermediates in the route of synthesis from the starting material to the drug substance.
The risk of carryover into the drug substance should be assessed for identified impurities that
are present in starting materials and intermediates and impurities that are reasonably expected
by-products in the route of synthesis from the starting material to the drug substance. As the
risk of carryover may be negligible for some impurities (e.g., those impurities in early
synthetic steps of long routes of synthesis), a risk-based justification could be provided for
the point in the synthesis after which these types of impurities should be evaluated for
mutagenic potential.
For starting materials that are introduced late in the synthesis of the drug substance (and
where the synthetic route of the starting material is known), the final steps of the starting
material synthesis should be evaluated for potential mutagenic impurities.
Actual impurities where the structures are known and potential impurities as defined above
should be evaluated for mutagenic potential as described in section VI (6).
B. 	Degradation Products (5.2)
Actual drug substance degradation products include those observed above the ICH Q3A
reporting threshold during storage of the drug substance in the proposed long-term storage
conditions and primary and secondary packaging. Actual degradation products in the drug
product include those observed above the ICH Q3B(R2) reporting threshold during storage of
the drug product in the proposed long-term storage conditions and primary and secondary
packaging, and also include those impurities that arise during the manufacture of the drug
product. Identification of actual degradation products is expected when the levels exceed the
identification thresholds outlined by ICH Q3A and Q3B(R2). It is acknowledged that some
degradation products below the identification threshold may also have been identified.
Potential degradation products in the drug substance and drug product are those that may be
reasonably expected to form during long-term storage conditions. Potential degradation
products include those that form above the ICH Q3A and Q3B(R2) identification thresholds
during accelerated stability studies (e.g., 40°C/75 percent relative humidity for 6 months) and
confirmatory photostability studies as described in the ICH guidance for industry Q1B
Photostability Testing of New Drug Substances and Products (November 1996) (Ref. 5), but
are yet to be confirmed in the drug substance or drug product under long-term storage
conditions in the primary packaging.
Knowledge of relevant degradation pathways can be used to help guide decisions on the
selection of potential degradation products to be evaluated for mutagenicity (e.g., from
degradation chemistry principles, relevant stress testing studies, and development stability
studies).

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Actual and potential degradation products likely to be present in the final drug substance or
drug product and where the structure is known should be evaluated for mutagenic potential as
described in section VI (6).
C. 	Considerations for Clinical Development (5.3)
It is expected that the impurity assessment described in sections V.A (5.1) and V.B (5.2)
applies to products in clinical development. However, it is acknowledged that the available
information is limited. For example, information from long-term stability studies and
photostability studies may not be available during clinical development, and thus,
information on potential degradation products may be limited. Additionally, the thresholds
outlined in ICH Q3A and Q3B(R2) do not apply to products in clinical development and
consequently fewer impurities will be identified.
VI. 	Hazard Assessment Elements (6)
Hazard assessment involves an initial analysis of actual and potential impurities by
conducting database and literature searches for carcinogenicity and bacterial mutagenicity
data to classify them as Class 1, 2, or 5 according to Table 1. If data for such a classification
are not available, an assessment of structure-activity relationships (SARs) that focuses on
bacterial mutagenicity predictions should be performed. This could lead to a classification
into Class 3, 4, or 5.
Table 1: Impurities Classification With Respect to Mutagenic and Carcinogenic
Potential and Resulting Control Actions
Class 	Definition
Proposed action for control
(details in sections VII (7)
and VIII (8))
1 	Known mutagenic carcinogens 	Control at or below compound-
specific acceptable limit
2 	Known mutagens with unknown
carcinogenic potential (bacterial
mutagenicity positive,* no rodent
carcinogenicity data)
Control at or below acceptable limits
(appropriate threshold of
toxicological concern (TTC))
3 	Alerting structure, unrelated to the structure
of the drug substance;
no mutagenicity data
Control at or below acceptable limits
(appropriate TTC) or conduct
bacterial mutagenicity assay;
if nonmutagenic = Class 5; if
mutagenic = Class 2
4 	Alerting structure, same alert in drug
substance or compounds related to the drug
substance (e.g., process intermediates),
which have been tested and are
nonmutagenic
Treat as nonmutagenic impurity

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Class 	Definition
Proposed action for control
(details in sections VII (7)
and VIII (8))
5 	No structural alerts, or alerting structure
with sufficient data to demonstrate lack of
mutagenicity or carcinogenicity
Treat as nonmutagenic impurity
*Or other relevant positive mutagenicity data indicative of DNA-reactivity related induction of gene mutations
(e.g., positive findings in in vivo gene mutation studies).
A computational toxicology assessment should be performed using (quantitative) SAR
((Q)SAR) methodologies that predict the outcome of a bacterial mutagenicity assay (Ref. 6).
Two (Q)SAR prediction methodologies that complement each other should be applied. One
methodology should be expert rule based, and the second methodology should be statistical
based. (Q)SAR models utilizing these prediction methodologies should follow the general
validation principles set forth by the Organization for Economic Co-operation and
Development (OECD).
The absence of structural alerts from two complementary (Q)SAR methodologies (expert rule
based and statistical) is sufficient to conclude that the impurity is of no mutagenic concern,
and no further testing is recommended (Class 5 in Table 1).
If warranted, the outcome of any computer system-based analysis can be reviewed with the
use of expert knowledge to provide additional supportive evidence on relevance of any
positive, negative, conflicting, or inconclusive prediction and provide a rationale to support
the final conclusion.
To follow up on a relevant structural alert (Class 3 in Table 1), either adequate control
measures could be applied or a bacterial mutagenicity assay with the impurity alone could be
conducted. An appropriately conducted negative bacterial mutagenicity assay (Note 2) would
overrule any structure-based concern, and no further genotoxicity assessments would be
recommended (Note 1). These impurities should be considered nonmutagenic (Class 5 in
Table 1). A positive bacterial mutagenicity result would warrant further hazard assessment
and/or control measures (Class 2 in Table 1). For instance, when levels of the impurity cannot
be controlled at an appropriate acceptable limit, it is recommended that the impurity be tested
in an in vivo gene mutation assay to understand the relevance of the bacterial mutagenicity
assay result under in vivo conditions. The selection of other in vivo genotoxicity assays
should be scientifically justified based on knowledge of the mechanism of action of the
impurity and expected target tissue exposure (Note 3). In vivo studies should be designed
taking into consideration existing ICH genotoxicity guidances. Results in the appropriate in
vivo assay may support setting compound-specific impurity limits.
An impurity with a structural alert that is shared (e.g., same structural alert in the same
position and chemical environment) with the drug substance or related compounds can be
considered as nonmutagenic (Class 4 in Table 1) if the testing of such material in the bacterial
mutagenicity assay was negative.

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VII. 	Risk Characterization (7)
As a result of hazard assessment described in section VI (6), each impurity will be assigned
to one of the five classes in Table 1. For impurities belonging in Classes 1, 2, and 3, the
principles of risk characterization used to derive acceptable intakes are described in this
section.
A. 	TTC-based Acceptable Intakes (7.1)
A TTC-based acceptable intake of a mutagenic impurity of 1.5 μg per person per day is
considered to be associated with a negligible risk (theoretical excess cancer risk of less than 1
in 100,000 over a lifetime of exposure) and can in general be used for most pharmaceuticals
as a default to derive an acceptable limit for control. This approach would usually be used for
mutagenic impurities present in pharmaceuticals for long-term treatment (greater than 10
years) and where no carcinogenicity data are available (Classes 2 and 3).
B. 	Acceptable Intakes Based on Compound-Specific Risk Assessments (7.2)
1. 	Mutagenic Impurities With Positive Carcinogenicity Data (Class 1 in Table 1)
(7.2.1)
Compound-specific risk assessments to derive acceptable intakes should be applied instead of
the TTC-based acceptable intakes where sufficient carcinogenicity data exist. For a known
mutagenic carcinogen, a compound-specific acceptable intake can be calculated based on
carcinogenic potency and linear extrapolation as a default approach. Alternatively, other
established risk assessment practices such as those used by international regulatory bodies
may be applied either to calculate acceptable intakes or to use already existing values
published by regulatory authorities (Note 4).
Compound-specific calculations for acceptable intakes can be applied case by case for
impurities, which are chemically similar to a known carcinogen compound class (class-
specific acceptable intakes) provided that a rationale for chemical similarity and supporting
data can be demonstrated (Note 5).
2. 	Mutagenic Impurities with Evidence for a Practical Threshold (7.2.2)
The existence of mechanisms leading to a dose response that is nonlinear or has a practical
threshold is increasingly recognized, not only for compounds that interact with non-DNA
targets but also for DNA-reactive compounds, whose effects may be modulated by, for
example, rapid detoxification before coming into contact with DNA, or by effective repair of
induced damage. The regulatory approach to such compounds can be based on the
identification of a no observed effect level (NOEL) and use of uncertainty factors (ICH
guidance for industry Q3C(R8) Impurities: Guidance for Residual Solvents (December 2021),
Ref. 7) to calculate a permissible daily exposure (PDE) when data are available.
The acceptable intakes derived from compound-specific risk assessments (section VII.B
(7.2)) can be adjusted for shorter duration of use in the same proportions as defined in the
following sections (sections VII.C.1 (7.3.1) and VII.C.2 (7.3.2)) or should be limited to not
more than 0.5 percent, whichever is lower. For example, if the compound-specific acceptable
intake is 15 μg/day for lifetime exposure, the less-than-lifetime limits (Table 2) can be

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increased to a daily intake of 100 μg (greater than 1 to 10 years’ treatment duration), 200 μg
(greater than 1 to 12 months) or 1,200 μg (less than 1 month). However, for a drug with a
maximum daily dose of, for instance, 100 milligrams (mg) the acceptable daily intake for the
less than 1 month’s duration would be limited to 0.5 percent (500 μg) rather than 1,200 μg.
C. 	Acceptable Intakes in Relation to LTL Exposure (7.3)
Standard risk assessments of known carcinogens assume that cancer risk increases as a
function of cumulative dose. Thus, cancer risk of a continuous low dose over a lifetime
would be equivalent to the cancer risk associated with an identical cumulative exposure
averaged over a shorter duration.
The TTC-based acceptable intake of 1.5 μg/day is considered to be protective for a lifetime of
daily exposure. To address LTL exposures to mutagenic impurities in pharmaceuticals, an
approach is applied in which the acceptable cumulative lifetime dose (1.5 μg/day times
25,550 days equals 38.3 mg) is uniformly distributed over the total number of exposure days
during LTL exposure. This would allow higher daily intake of mutagenic impurities than
would be the case for lifetime exposure and still maintain comparable risk levels for daily and
nondaily treatment regimens. Table 2 is derived from the above concepts and illustrates the
acceptable intakes for LTL to lifetime exposures for clinical development and marketing. In
the case of intermittent dosing, the acceptable daily intake should be based on the total
number of dosing days instead of the time interval over which the doses were administered
and that number of dosing days should be related to the relevant duration category in Table 2.
For example, a drug administered once per week for 2 years (i.e., 104 dosing days) would
have an acceptable intake per dose of 20μg.
Table 2: Acceptable Intakes for an Individual Impurity
Duration of
Treatment
< 1
Month
>1 to 12
Months
>1 to 10
Years
>10 Years to
Lifetime
Daily intake
[μg/day] 120 	20 	10 	1.5
1. 	Clinical Development (7.3.1)
Using this LTL concept, acceptable intakes of mutagenic impurities are recommended for
limited treatment periods during clinical development of up to 1 month, 1 to 12 months, and
more than 1 year up to completion of phase 3 clinical trials (Table 2). These adjusted
acceptable intake values maintain a 10 -6 (1 in 1 million) risk level in early clinical
development when benefit has not yet been established and a 10-5 risk level for later stages in
development (Note 6).
An alternative approach to the strict use of an adjusted acceptable intake for any mutagenic
impurity could be applied for phase 1 clinical trials for dosing up to 14 days. For this
approach, only impurities that are known mutagenic carcinogens (Class 1) and known
mutagens of unknown carcinogenic potential (Class 2), as well as impurities in the cohort of
concern chemical class, should be controlled (see section VIII (8)) to acceptable limits as
described in section VII (7). All other impurities would be treated as nonmutagenic

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impurities. This includes impurities that contain structural alerts (Class 3), which alone would
not trigger action for an assessment for this limited phase 1 duration.
2. 	Marketed Products (7.3.2)
The treatment duration categories with acceptable intakes in Table 2 for marketed products
are intended to be applied to anticipated exposure durations for the great majority of patients.
The proposed intakes along with various scenarios for applying those intakes are described in
Table 4, Note 7. In some cases, a subset of the population of patients may extend treatment
beyond the marketed drug’s categorical upper limit (e.g., treatment exceeding 10 years for an
acceptable intake of 10 μg/day, perhaps receiving 15 years of treatment). This would result in
a negligible increase (in the example given, a fractional increase to 1.5/100,000) compared to
the overall calculated risk for the majority of patients treated for 10 years.
D. 	Acceptable Intakes for Multiple Mutagenic Impurities (7.4)
The TTC-based acceptable intakes should be applied to each individual impurity. When there
are two Class 2 or Class 3 impurities, individual limits apply. When there are three or more
Class 2 or Class 3 impurities specified on the drug substance specification, total mutagenic
impurities should be limited as described in Table 3 for clinical development and marketed
products.
For combination products each active ingredient should be regulated separately.
Table 3: Acceptable Total Daily Intakes for Multiple Impurities
Duration of
treatment
< 1 month 	>1 to 12 months >1 to 10 Years 	>10 Years to
Lifetime
Total daily
intake
[μg/day]
120 	60 	30 	5
Only specified Class 2 and Class 3 impurities on the drug substance specification are
included in the calculation of the total limit. However, impurities with compound-specific or
class-related acceptable intake limits (Class 1) should not be included in the total limits of
Class 2 and Class 3 impurities. Also, degradation products, which form in the drug product,
would be controlled individually, and a total limit would not be applied.
E. 	Exceptions and Flexibility in Approaches (7.5)
• 	Higher acceptable intakes may be justified when human exposure to the impurity will
be much greater from other sources, e.g., food, endogenous metabolism (e.g.,
formaldehyde).
• 	Case-by-case exceptions to the use of the appropriate acceptable intake can be
justified in cases of severe disease, reduced life expectancy, late onset but chronic
disease, or with limited therapeutic alternatives.

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• 	Compounds from some structural classes of mutagens can display extremely high
carcinogenic potency (cohort of concern) (i.e., aflatoxin-like-, N-nitroso-, and alkyl-
azoxy structures). If these compounds are found as impurities in pharmaceuticals,
acceptable intakes for these high-potency carcinogens would likely be significantly
lower than the acceptable intakes defined in this guidance. Although the principles of
this guidance can be used, a case-by-case approach using, for example,
carcinogenicity data from closely related structures, if available, should usually be
developed to justify acceptable intakes for pharmaceutical development and marketed
products.
The above risk approaches described in section VII (7) are applicable to all routes of
administration, and no corrections to acceptable intakes are generally warranted. Exceptions
to consider may include situations where data justify route-specific concerns that should be
evaluated case by case. These approaches are also applicable to all subject populations based
upon the conservative nature of the risk approaches being applied.
VIII. 	CONTROL (8)
A control strategy is a planned set of controls, derived from current product and process
understanding that assures process performance and product quality (ICH guidance for
industry Q10 Pharmaceutical Quality System (ICH Q10) (April 2009), Ref. 8). A control
strategy can include, but is not limited to, the following:
• 	Controls on material attributes (including raw materials, starting materials,
intermediates, reagents, solvents, primary packaging materials);
• 	Facility and equipment operating conditions;
• 	Controls implicit in the design of the manufacturing process;
• 	In-process controls (including in-process tests and process parameters); and
• 	Controls on drug substance and drug product (e.g., release testing).
When an impurity has been characterized as Class 1, 2, or 3 in Table 1, it is important to
develop a control strategy that assures that the level of this impurity in the drug substance and
drug product is below the acceptable limit. A thorough knowledge of the chemistry
associated with the drug substance manufacturing process, and of the drug product
manufacturing process, along with an understanding of the overall stability of the drug
substance and drug product is fundamental to developing the appropriate controls.
Developing a strategy to control mutagenic impurities in the drug product is consistent with
risk management processes identified in the ICH guidance for industry Q9(R1) Quality Risk
Management (May 2023) (Ref. 9). A control strategy that is based on product and process
understanding and utilization of risk management principles will lead to a combination of

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process design and control and appropriate analytical testing, which can also provide an
opportunity to shift controls upstream and minimize the need for end-product testing.
A. 	Control of Process-Related Impurities (8.1)
There are four potential approaches to development of a control strategy for a drug substance:
Option 1
Include a test for the impurity in the drug substance specification with an acceptance criterion
at or below the acceptable limit using an appropriate analytical procedure.
For an Option 1 control approach, it is possible to apply periodic verification testing per the
ICH guidance for industry Q6A Specifications: Test Procedures and Acceptance Criteria for
New Drug Substances and New Drug Products: Chemical Substances (ICH Q6A) (December
2000) (Ref. 10). Periodic verification testing is justified when it can be shown that levels of
the mutagenic impurity in the drug substance are less than 30 percent of the acceptable limit
for at least six consecutive pilot scale or three consecutive production scale batches. If this
condition is not fulfilled, a routine test in the drug substance specification is recommended.
See section VIII.C (8.3) for additional considerations.
Option 2
Include a test for the impurity in the specification for a raw material, starting material, or
intermediate, or as an in-process control, with an acceptance criterion at or below the
acceptable limit using an appropriate analytical procedure.
Option 3
Include a test for the impurity in the specification for a raw material, starting material, or
intermediate, or as an in-process control, with an acceptance criterion above the acceptable
limit of the impurity in the drug substance, using an appropriate analytical procedure coupled
with demonstrated understanding of fate and purge and associated process controls that
assure the level in the drug substance is below the acceptable limit without the need for any
additional testing later in the process.
This option can be justified when the level of the impurity in the drug substance will be less
than 30 percent of the acceptable limit by review of data from laboratory scale experiments
(spiking experiments are encouraged) and where necessary supported by data from pilot scale
or commercial scale batches. See case examples 1 and 2 in Appendix 2. Alternative
approaches can be used to justify Option 3.
Option 4
Understand process parameters and impact on residual impurity levels (including fate and
purge knowledge) with sufficient confidence that the level of the impurity in the drug
substance will be below the acceptable limit such that no analytical testing is recommended
for this impurity (i.e., the impurity does not need to be listed on any specification).

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A control strategy that relies on process controls in lieu of analytical testing can be
appropriate if the process chemistry and process parameters that impact levels of mutagenic
impurities are understood and the risk of an impurity residing in the final drug substance
above the acceptable limit is determined to be negligible. In many cases justification of this
control approach based on scientific principles alone is sufficient. Elements of a scientific
risk assessment can be used to justify an Option 4 approach. The risk assessment can be
based on physicochemical properties and process factors that influence the fate and purge of
an impurity including chemical reactivity, solubility, volatility, Ionizability, and any physical
process steps designed to remove impurities. The result of this risk assessment might be
shown as an estimated purge factor for clearance of the impurity by the process (Ref. 11).
Option 4 is especially useful for those impurities that are inherently unstable (e.g., thionyl
chloride that reacts rapidly and completely with water) or for those impurities that are
introduced early in the synthesis and are effectively purged.
In some cases an Option 4 approach can be appropriate when the impurity is known to form,
or is introduced late in the synthesis; however, process-specific data should then be provided
to justify this approach.
B. 	Considerations for Control Approaches (8.2)
For Option 4 approaches where justification based on scientific principles alone is not
considered sufficient, as well as for Option 3 approaches, analytical data to support the
control approach is expected. This could include, as appropriate, information on the structural
changes to the impurity caused by downstream chemistry (fate), analytical data on pilot scale
batches and, in some cases, laboratory scale studies with intentional addition of the impurity
(spiking studies). In these cases, it is important to demonstrate that the fate/purge argument
for the impurity is robust and will consistently assure a negligible probability of an impurity
residing in the final drug substance above the acceptable limit. Where the purge factor is
based on developmental data, it is important to address the expected scale dependence or
independence. In the case that the small scale model used in the development stage is
considered to not represent the commercial scale, confirmation of suitable control in pilot
scale and/or initial commercial batches is generally appropriate. The need for data from
pilot/commercial batches is influenced by the magnitude of the purge factor calculated from
laboratory or pilot scale data, point of entry of the impurity, and knowledge of downstream
process purge points.
If Options 3 and 4 cannot be justified, then a test for the impurity on the specification for a
raw material, starting material or intermediate, or as an in-process control (Option 2) or drug
substance (Option 1) at the acceptable limit should be included. For impurities introduced in
the last synthetic step, an Option 1 control approach would be expected unless otherwise
justified.
The application of as low as reasonably practicable (ALARP) is not necessary if the level of
the mutagenic impurity is below acceptable limits. Similarly, it is not necessary to
demonstrate that alternate routes of synthesis have been explored.
In cases where control efforts cannot reduce the level of the mutagenic impurity to below the
acceptable limit and levels are ALARP, a higher limit may be justified based on a benefit-risk
analysis.

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C. 	Considerations for Periodic Testing (8.3)
The above options include situations where a test is recommended to be included in the
specification, but where routine measurement for release of every batch may not be
necessary. This approach, referred to as periodic or skip testing in ICH Q6A could also be
called periodic verification testing. This approach may be appropriate when it can be
demonstrated that processing subsequent to impurity formation/introduction clears the
impurity. It should be noted that allowance of periodic verification testing is contingent upon
use of a process that is under a state of control (i.e., produces a quality product that
consistently meets specifications and conforms to an appropriately established facility,
equipment, processing, and operational control regimen). If upon testing, the level of the
mutagenic impurity fails to meet the acceptance criteria established for the periodic test, the
drug producer should immediately commence full testing (i.e., testing of every batch for the
attribute specified) until the cause of the failure has been conclusively determined, corrective
action has been implemented, and the process is again documented to be in a state of control.
As noted in ICH Q6A, regulatory authorities should be notified of a periodic verification test
failure to evaluate the benefit/risk of previously released batches that were not tested.
D. 	Control of Degradation Products (8.4)
For a potential degradation product that has been characterized as mutagenic, it is important
to understand if the degradation pathway is relevant to the drug substance and drug product
manufacturing processes and/or their proposed packaging and storage conditions. A well-
designed accelerated stability study (e.g., 40°C/75 percent relative humidity, 6 months) in the
proposed packaging, with appropriate analytical procedures is recommended to determine the
relevance of the potential degradation product. Alternatively, well-designed, kinetically
equivalent shorter term stability studies at higher temperatures in the proposed commercial
package may be used to determine the relevance of the degradation pathway before initiating
longer term stability studies. This type of study would be especially useful to understand the
relevance of those potential degradation products that are based on knowledge of potential
degradation pathways but not yet observed in the product.
Based on the result of these accelerated studies, if it is anticipated that the degradation
product will form at levels approaching the acceptable limit under the proposed packaging
and storage conditions, then efforts to control formation of the degradation product is
expected. In these cases, monitoring for the drug substance or drug product degradation
product in long-term primary stability studies at the proposed storage conditions (in the
proposed commercial pack) is expected unless otherwise justified. Whether or not a
specification limit for the mutagenic degradation product is appropriate will generally depend
on the results from these stability studies.
If it is anticipated that formulation development and packaging design options are unable to
control mutagenic degradation product levels to less than the acceptable limit and levels are
ALARP, a higher limit can be justified based on a benefit-risk analysis.
E. 	Lifecycle Management (8.5)
This section is intended to apply to those products approved after the issuance of this
guidance.

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The quality system elements and management responsibilities described in ICH Q10 are
intended to encourage the use of science-based and risk-based approaches at each lifecycle
stage, thereby promoting continual improvement across the entire product lifecycle. Product
and process knowledge should be managed from development through the commercial life of
the product up to and including product discontinuation.
The development and improvement of a drug substance or drug product manufacturing
process usually continues over its lifecycle. Manufacturing process performance, including
the effectiveness of the control strategy, should be periodically evaluated. Knowledge gained
from commercial manufacturing can be used to further improve process understanding and
process performance and to adjust the control strategy.
Any proposed change to the manufacturing process should be evaluated for the impact on the
quality of drug substance and drug product. This evaluation should be based on
understanding of the manufacturing process and should determine if appropriate testing to
analyze the impact of the proposed changes is required. Additionally, improvements in
analytical procedures may lead to structural identification of an impurity. In those cases the
new structure would be assessed for mutagenicity as described in this guidance.
Throughout the lifecycle of the product, it will be important to reassess if testing is
recommended when intended or unintended changes occur in the process. This applies when
there is no routine monitoring at the acceptable limit (Option 3 or Option 4 control
approaches) or when applying periodic rather than batch-by-batch testing. This testing should
be performed at an appropriate point in the manufacturing process.
In some cases, the use of statistical process control and trending of process measurements can
be useful for continued suitability and capability of processes to provide adequate control on
the impurity. Statistical process control can be based on process parameters that influence
impurity formation or clearance, even when that impurity is not routinely monitored (e.g.,
Option 4).
All changes should be subject to internal change management processes as part of the quality
system (ICH Q10). Changes to information filed and approved in a dossier should be reported
to regulatory authorities in accordance with regional regulations and guidances.
F. 	Considerations for Clinical Development (8.6)
It is recognized that product and process knowledge increases over the course of
development, and therefore, it is expected that data to support control strategies in the clinical
development trial phases will be less than at the marketing registration phase. A risk-based
approach based on process chemistry fundamentals is encouraged to prioritize analytical
efforts on those impurities with the highest likelihood of being present in the drug substance
or drug product. Analytical data may not be expected to support early clinical development
when the likelihood of an impurity being present is low, but in a similar situation analytical
data may be appropriate to support the control approach for the marketing application. It is
also recognized that commercial formulation design occurs later in clinical development and
therefore efforts associated with drug product degradation products will be limited in the
earlier phases.

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IX. 	DOCUMENTATION (9)
Information relevant to the application of this guidance should be provided at the following
stages:
A. 	Clinical Trial Applications (9.1)
• 	It is expected that the number of structures assessed for mutagenicity and the
collection of analytical data will both increase throughout the clinical development
period.
• 	For phase 1 studies of 14 days or less, a description of efforts to mitigate risks of
mutagenic impurities focused on Class 1 and Class 2 impurities and those in the
cohort of concern as outlined in section VII (7) should be included. For phase 1
clinical trials greater than 14 days and for phase 2a clinical trials additionally Class 3
impurities that require analytical controls should be included.
• 	For phase 2b and phase 3 clinical development trials, a list of the impurities assessed
by (Q)SAR should be included, and any Class 1, Class 2, or Class 3 actual and
potential impurities should be described along with plans for control. The in silico
(Q)SAR systems used to perform the assessments should be described. The results of
bacterial mutagenicity tests of actual impurities should be reported.
• 	Chemistry arguments may be appropriate instead of analytical data for potential
impurities that present a low likelihood of being present as described in section VIII.
F (8.6).
B. 	Common Technical Document (Marketing Application) (9.2)
• 	For actual and potential process-related impurities and degradation products where
assessments according to this guidance are conducted, the mutagenic impurity
classification and rationale for this classification should be provided:
 This would include the results and description of in silico (Q)SAR systems used
and, as appropriate, supporting information to arrive at the overall conclusion for
Class 4 and Class 5 impurities.
 When bacterial mutagenicity assays were performed on impurities, study reports
should be provided for bacterial mutagenicity assays on impurities.
• 	Justification for the proposed specification and the approach to control should be
provided (e.g., the ICH guidance for industry Q11 Development and Manufacture of
Drug Substances (Chemical Entities and Biotechnological/Biological Entities)
(November 2012) example Table 5b at 29–30, Ref. 12). For example, this information
could include the acceptable intake, the location, and sensitivity of relevant routine
monitoring. For Option 3 and Option 4 control approaches, a summary of knowledge
of the purge factor and identification of factors providing control (e.g., process steps,
solubility in wash solutions) is important.

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NOTES
Note 1 The International Council for Harmonisation (ICH) guidance for industry M7(R2)
Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals
to Limit Potential Carcinogenic Risk (ICH M7(R2)) recommendations provide a state-
of-the-art approach for assessing the potential of impurities to induce point mutations
and ensure that such impurities are controlled to safe levels so that below or above the
ICH Q3A and Q3B(R2) qualification threshold no further qualification for mutagenic
potential is required. This includes the initial use of (quantitative) structure-activity
relationship ((Q)SAR) tools to predict bacterial mutagenicity. In cases where the
amount of the impurity exceeds 1 milligram (mg) daily dose for chronic
administration, evaluation of genotoxic potential as recommended in ICH
Q3A/Q3B(R2) could be considered. In cases where the amount of the impurity is
equal to or less than 1 mg, no further genotoxicity testing is required regardless of
other qualification thresholds.
Note 2 To assess the mutagenic potential of impurities, a single bacterial mutagenicity assay
can be carried out with a fully adequate protocol according to the ICH guidance for
industry S2(R1) Genotoxicity Testing and Data Interpretation for Pharmaceuticals
Intended for Human Use (June 2012) and OECD Test 471 guideline (Ref. 13, 14).
The assays are expected to be performed in compliance with good laboratory practice
(GLP) regulations; however, lack of full GLP compliance does not necessarily mean
that the data cannot be used to support clinical trials and marketing authorizations.
Such deviations should be described in the study report. For example, the test article
may not be prepared or analyzed in compliance with GLP regulations. In some cases,
the selection of bacterial tester strains may be limited to those proven to be sensitive
to the identified alert. For impurities that are not feasible to isolate or synthesize or
when compound quantity is limited, it may not be possible to achieve the highest test
concentrations recommended for an ICH-compliant bacterial mutagenicity assay
according to the current testing guidelines. In this case, bacterial mutagenicity testing
could be carried out using a miniaturized assay format with proven high concordance
to the ICH-compliant assay to enable testing at higher concentrations with
justification.
Note 3 Tests to Investigate the In Vivo Relevance of In Vitro Mutagens (Positive
Bacterial Mutagenicity)
In Vivo Test Factors to Justify Choice
of Test as Fit-for-Purpose
Transgenic mutation assays 	• 	For any bacterial mutagenicity positive. Justify selection
of assay tissue/organ
Pig-a assay
(blood)
• 	For directly acting mutagens (bacterial mutagenicity
positive without S9) *
Micronucleus test
(blood or bone marrow)
• 	For directly acting mutagens (bacterial mutagenicity
positive without S9) and compounds known to be
clastogenic*

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In Vivo Test Factors to Justify Choice
of Test as Fit-for-Purpose
Rat liver unscheduled DNA
synthesis (UDS) test
• 	In particular for bacterial mutagenicity positive with S9
only
• 	Responsible liver metabolite known
 To be generated in test species used
 To induce bulky adducts
Comet assay 	• 	Justification needed (chemical class-specific mode of
action to form alkaline labile sites or single-strand
breaks as preceding DNA damage that can potentially
lead to mutations)
• 	Justify selection of assay tissue/organ
Others 	• 	With convincing justification
* For indirect acting mutagens (requiring metabolic activation), adequate exposure to metabolite(s) should
be demonstrated.
Note 4 Example of linear extrapolation from the TD50
It is possible to calculate a compound-specific acceptable intake based on rodent
carcinogenicity potency data such as TD50 values (doses giving a 50 percent tumor
incidence equivalent to a cancer risk probability level of 1:2). Linear extrapolation to
a probability of 1 in 100,000 (i.e., the accepted lifetime risk level used) is achieved by
simply dividing the TD50 by 50,000. This procedure is similar to that employed for
derivation of the TTC.
Calculation example: Ethylene oxide
TD50 values for ethylene oxide according to the Carcinogenic Potency Database are
21.3 mg/kilogram (kg) body weight/day (rat) and 63.7 mg/kg body weight/day
(mouse). For the calculation of an acceptable intake, the lower (i.e., more
conservative) value of the rat is used.
To derive a dose to cause tumors in 1 in 100,000 animals, divide by 50,000:
21.3 mg/kg ÷ 50,000 = 0.42 μg/kg
To derive a total human daily dose:
0.42 μg/kg/day x 50 kg body weight = 21.3 μg/person/day
Hence, a daily lifelong intake of 21.3 μg ethylene oxide would correspond to a
theoretical cancer risk of 10-5 and therefore be an acceptable intake when present as
an impurity in a drug substance.
Alternative methods and published regulatory limits for cancer risk assessment
As an alternative of using the most conservative TD50 value from rodent
carcinogenicity studies irrespective of its relevance to humans, an in-depth

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toxicological expert assessment of the available carcinogenicity data can be done to
initially identify the findings (species, organ, etc.) with highest relevance to human
risk assessment as a basis for deriving a reference point for linear extrapolation. Also,
to better take into account directly the shape of the dose-response curve, a benchmark
dose such as a benchmark dose lower confidence limit 10 percent (BMDL10, an
estimate of the lowest dose which is 95 percent certain to cause no more than a 10
percent cancer incidence in rodents) may be used instead of TD50 values as a
numerical index for carcinogenic potency. Linear extrapolation to a probability of 1 in
100,000 (i.e., the accepted lifetime risk level used) is then achieved by simply
dividing the BMDL10 by 10,000.
Compound-specific acceptable intakes can also be derived from published
recommended values from internationally recognized bodies such as the World Health
Organization (WHO, International Programme on Chemical Safety (IPCS) Cancer
Risk Assessment Programme) and others using the appropriate 10-5 lifetime risk
level. In general, a regulatory limit that is applied should be based on the most current
and scientifically supported data and/or methodology.
Note 5 A compound-specific calculation of acceptable intakes for mutagenic impurities may
be applied for mutagenic impurities (without carcinogenicity data), which are
structurally similar to a chemically defined class of known carcinogen. For example,
factors that are associated with the carcinogenic potency of monofunctional alkyl
chlorides have been identified (Ref. 15) and can be used to modify the safe acceptable
intake of monofunctional alkyl chlorides, a group of alkyl chlorides commonly used
in drug synthesis. Compared to multifunctional alkyl chlorides the monofunctional
compounds are much less potent carcinogens with TD50 values ranging from 36 to
1810 mg/kg/day (n=15; epichlorohydrin with two distinctly different functional
groups is excluded). A TD50 value of 36 mg/kg/day can thus be used as a still very
conservative class-specific potency reference point for calculation of acceptable
intakes for monofunctional alkyl chlorides. This potency level is at least tenfold lower
than the TD50 of 1.25 mg/kg/day corresponding to the default lifetime TTC (1.5
μg/day) and therefore justifies lifetime and LTL daily intakes for monofunctional
alkyl chlorides 10 times the default ones.
Note 6 Establishing LTL acceptable intakes for mutagenic impurities in pharmaceuticals has
precedent in the establishment of the staged TTC limits for clinical development (Ref.
16). The calculation of LTL acceptable intakes (AI) is predicated on the principle of
Haber’s rule, a fundamental concept in toxicology where concentration (C) multiplied
by time (T) equals a constant (k). Therefore, the carcinogenic effect is based on both
dose and duration of exposure.

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Figure 1: Illustration of calculated daily dose of a mutagenic impurity corresponding
to a theoretical 1:100,000 cancer risk as a function of duration of treatment in
comparison to the acceptable intake levels as recommended in section VII.C (7.3).
The solid line in Figure 1 represents the linear relationship between the amount of
daily intake of a mutagenic impurity corresponding to a 10-5 cancer risk and the
number of treatment days. The calculation is based on the TTC level as applied in this
guidance for lifelong treatment, i.e., 1.5 μg per person per day using the formula:
Less-than-lifetime AI = 1.5 μg x (365 days x 70 years lifetime = 25,550)
Total number of treatment days
The calculated daily intake levels would thus be 1.5 μg for treatment duration of 70
years, 10 μg for 10 years, 100 μg for 1 year, 1270 μg for 1 month, and approximately
38.3 mg as a single dose, all resulting in the same cumulative intake and therefore
theoretically in the same cancer risk (1 in 100,000).
The dashed step-shaped curve represents the actual daily intake levels adjusted to
less-than-lifetime exposure as recommended in section VII (7) of this guidance for
products in clinical development and marketed products. These proposed levels are in
general significantly lower than the calculated values thus providing safety factors
that increase with shorter treatment durations.
The proposed accepted daily intakes are also in compliance with a 10-6 cancer risk
level if treatment durations are not longer than 6 months and are therefore applicable
in early clinical trials with volunteers/subjects where benefit has not yet been
established. In this case the safety factors as shown in the upper graph would be
reduced by a factor of 10.

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Note 7 Table 4: Examples of Clinical Use Scenarios With Different Treatment
Durations for Applying Acceptable Intakes
Scenario* Acceptable Intake
(μg/day)
Treatment duration of < 1 month: e.g., drugs used in emergency
procedures (antidotes, anesthesia, acute ischemic stroke), actinic
keratosis, treatment of lice
120
Treatment duration of > 1–12 months: e.g., anti-infective therapy
with maximum up to 12 months treatment (hepatitis C virus),
parenteral nutrients, prophylactic flu drugs (~5 months), peptic ulcer,
assisted reproductive technology (ART), preterm labor, preeclampsia,
presurgical (hysterectomy) treatment, fracture healing (these are acute
use but with long half-lives)
20
Treatment duration of >1–10 years: e.g., stage of disease with short
life expectancy (severe Alzheimer’s disease), nongenotoxic anticancer
treatment being used in a patient population with longer term survival
(breast cancer, chronic myelogenous leukemia), drugs specifically
labeled for less than 10 years of use, drugs administered intermittently
to treat acute recurring symptoms** (chronic herpes, gout attacks,
substance dependence such as smoking cessation), macular
degeneration
10
Treatment duration of >10 years to lifetime: e.g., chronic use
indications with high likelihood for lifetime use across broader age
range (hypertension, dyslipidemia, asthma, Alzheimer’s disease
(except severe Alzheimer’s disease), hormone therapy (e.g., growth
hormone, thyroid hormone, parathyroid hormone), lipodystrophy,
schizophrenia, depression, psoriasis, atopic dermatitis, chronic
obstructive pulmonary disease (COPD), cystic fibrosis, seasonal and
perennial allergic rhinitis, HIV*** )
1.5
* This table shows general examples; each example should be examined on a case-by-case basis. For
example, 10 μg/day may be acceptable in cases where the life expectancy of the patient may be limited
(e.g., severe Alzheimer’s disease) even though the drug use could exceed a 10-year duration.
** Intermittent use over a period greater than 10 years but based on calculated cumulative dose it falls under
the greater than 1 to 10 years category.
*** Changed in this guidance (ICH M7(R2)) from 1 to 10 years to greater than10 years to lifetime because of
clinical treatment advances. See the ICH guidance for industry M7(R2) Assessment and Control of DNA
Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk: Questions and
Answers (July 2023).

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23
GLOSSARY
Acceptable intake:
In the context of this guidance, an intake level that poses negligible cancer risk, or for
serious/life-threatening indications where risk and benefit are appropriately balanced.
Acceptable limit:
Maximum acceptable concentration of an impurity in a drug substance or drug product
derived from the acceptable intake and the daily dose of the drug.
Acceptance criterion:
Numerical limits, ranges, or other suitable measures for acceptance of the results of analytical
procedures.
Control strategy:
A planned set of controls, derived from current product and process understanding that
ensures process performance and product quality. The controls can include parameters and
attributes related to drug substance and drug product materials and components, facility and
equipment operating conditions, in-process controls, finished product specifications, and the
associated methods and frequency of monitoring and control.
Cumulative intake:
The total intake of a substance that a person is exposed to over time.
Degradation product:
A molecule resulting from a chemical change in the drug molecule brought about over time
and/or by the action of light, temperature, pH, or water or by reaction with an excipient
and/or the immediate container/closure system.
DNA-reactive:
The potential to induce direct DNA damage through chemical reaction with DNA.
Expert knowledge:
In the context of this guidance, expert knowledge can be defined as a review of preexisting
data and the use of any other relevant information to evaluate the accuracy of an in silico
model prediction for mutagenicity.
Genotoxicity:
A broad term that refers to any deleterious change in the genetic material regardless of the
mechanism by which the change is induced.

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24
Impurity:
Any component of the drug substance or drug product that is not the drug substance or an
excipient.
Mutagenic impurity:
An impurity that has been demonstrated to be mutagenic in an appropriate mutagenicity test
model (e.g., bacterial mutagenicity assay).
Periodic verification testing:
Also known as periodic or skip testing in the International Council for Harmonisation
guidance for industry Q6A Specifications: Test Procedures and Acceptance Criteria for New
Drug Substances and New Drug Products: Chemical Substances (December 2000).1
(Q)SAR and SAR:
In the context of this guidance, refers to the relationship between the molecular (sub)
structure of a compound and its mutagenic activity using (quantitative) structure-activity
relationships derived from experimental data.
Purge factor:
Purge reflects the ability of a process to reduce the level of an impurity, and the purge factor
is defined as the level of an impurity at an upstream point in a process divided by the level of
an impurity at a downstream point in a process. Purge factors may be measured or predicted.
Structural alert:
In the context of this guidance, a chemical grouping or molecular (sub) structure, which is
associated with mutagenicity.
1 We update guidances periodically. To make sure you have the most recent version of a guidance, check the
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.

Contains Nonbinding Recommendations
25
REFERENCES
1. 	International Council for Harmonisation (ICH) guidance for industry Q3A Impurities
in New Drug Substances (Revision 2) (June 2008)1
2. 	ICH guidance for industry Q3B(R2) Impurities in New Drug Products (August 2006)
3. 	ICH guidance for industry M3(R2) Nonclinical Safety Studies for the Conduct of
Human Clinical Trials and Marketing Authorization for Pharmaceuticals (January
2010)
4. 	ICH guidance for industry S9 Nonclinical Evaluation for Anticancer Pharmaceuticals
(March 2010)
5. 	ICH guidance for industry Q1B Photostability Testing of New Drug Substances and
Products (November 1996)
6. 	Sutter A, Amberg A, Boyer S, Brigo A, Contrera JF, Custer LL, Dobo KL, Gervais V,
Glowienke S, van Gompel J, Greene N, Muster W, Nicolette J, Reddy MV, Thybaud
V, Vock E, White AT, and Müller L, 2013, Use of In Silico Systems and Expert
Knowledge for Structure-Based Assessment of Potentially Mutagenic Impurities,
Regul Toxicol Pharmacol, 67(1):39–52.
7. 	ICH guidance for industry Q3C(R8): Impurities: Guidance for Residual Solvents
(December 2021)
8. 	ICH guidance for industry Q10 Pharmaceutical Quality System (April 2009)
9. 	ICH guidance for industry Q9(R1) Quality Risk Management (May 2023)
10. ICH guidance for industry Q6A Specifications: Test Procedures and Acceptance
Criteria for New Drug Substances and New Drug Products: Chemical Substances
(December 2000)
11. Teasdale A, Elder D, Chang S-J, Wang S, Thompson R, Benz N, and Sanchez Flores
I, 2013, Risk Assessment of Genotoxic Impurities in New Chemical Entities:
Strategies to Demonstrate Control, Org Process Res Dev;17:221–230.
12. ICH guidance for industry Q11 Development and Manufacture of Drug Substances
(November 2012)
13. ICH guidance for industry S2(R1) Genotoxicity Testing and Data Interpretation for
Pharmaceuticals Intended for Human Use (June 2012)
14. Test 471. Bacterial Reverse Mutation Test Organization for Economic Co-operation
and Development Guideline for Testing of Chemicals Section 4, July 1997, available
at https://www.oecd.org/chemicalsafety/risk-assessment/1948418.pdf.
1 We update guidances periodically. To make sure you have the most recent version of a guidance, check the
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.

Contains Nonbinding Recommendations
26
15. Brigo A and Müller L, 2011, Development of the Threshold of Toxicological Concern
Concept and Its Relationship to Duration of Exposure, in Genotoxic Impurities (Ed.
A. Teasdale), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi:
10.1002/9780470929377.ch2
16. Müller L, Mauthe RJ, Riley CM, Andino MM, De Antonis D, Beels C, DeGeorge J,
De Knaep AGM, Ellison D, Fagerland JA, Frank R, Fritschel B, Galloway S, Harpur
E, Humfrey CDN, Jacks ASJ, Jagota N, Mackinnon J, Mohan G, Ness DK,
O’Donovan MR, Smith MD, Vudathala G, and Yotti L, 2006, A Rationale for
Determining, Testing, and Controlling Specific Impurities in Pharmaceuticals That
Possess Potential for Genotoxicity, Regul Toxicol Pharmacol, 44:198–211.

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APPENDIX 1: SCOPE SCENARIOS
FOR APPLICATION OF THE ICH M7(R2) GUIDANCE1
Scenario
Applies to
Drug
Substance
Applies
to Drug
Product
Comments
Registration of new drug
substances and associated
drug product.
Yes 	Yes 	Primary intent of the ICH M7(R2)
guidance.
Clinical trial applications
for new drug substances
and associated drug
product.
Yes 	Yes 	Primary intent of the ICH M7(R2)
guidance.
Clinical trial applications
for new drug substances
for an anticancer drug
per the ICH guidance
for industry S9
Nonclinical Evaluation
for Anticancer
Pharmaceuticals (March
2010) (ICH S9).
No 	No 	Out of scope of the ICH M7(R2)
guidance.
Clinical trial applications
for new drug substances
for an orphan drug.
Yes 	Yes 	There may be exceptions on a case-
by- case basis for higher impurity
limits.
Clinical trial application
for a new drug product
using an existing drug
substance where there are
no changes to the drug
substance manufacturing
process.
No 	Yes 	Retrospective application of the ICH
M7(R2) guidance is not intended for
marketed products unless there are
changes made to the synthesis.
Because no changes are made to the
drug substance synthesis, the drug
substance would not require
reevaluation. Because the drug
product is new, application of the
ICH M7(R2) guidance is expected.
A new formulation of an
approved drug substance
is filed.
No 	Yes 	See section IV.B (4.2) of the ICH
M7(R2) guidance.
A product that is
previously approved in a
member region is filed for
the first time in a different
member region. The
product is unchanged.
Yes 	Yes 	Because there is no mutual
recognition, an existing product in
one member region filed for the first
time in another member region
would be considered a new product.
1 International Council for Harmonisation (ICH) guidance for industry M7(R2) Assessment and Control of DNA
Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk (ICH M7(R2)).

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Scenario
Applies to
Drug
Substance
Applies
to Drug
Product
Comments
A new supplier or new
site of the drug substance
is registered. There are no
changes to the
manufacturing process
used in this registered
application.
No 	No 	As long as the synthesis of the drug
substance is consistent with
previously approved methods, then
reevaluation of mutagenic impurity
risk is not necessary. The applicant
would need to demonstrate that no
changes have been made to a
previously approved process/product.
See section IV.A (4.1) of the ICH
M7(R2) guidance.
An existing product
(approved after the
issuance of ICH M7(R2)
with higher limits based
on ICH S9) associated
with an advanced cancer
indication is now
registered for use in a
nonlife-threatening
indication.
Yes 	Yes 	Since the patient population and
acceptable cancer risk have changed,
the previously approved impurity
control strategy and limits will warrant
reevaluation. See section IV.C (4.3) of
ICH M7(R2).
New combination product
is filed that contains one
new drug substance and
an existing drug substance.
Yes (new
drug
substance)
No
(existing
drug
substance)
Yes 	ICH M7(R2) would apply to the new
drug substance. For the existing drug
substance, retrospective application
of ICH M7(R2) to existing products
is not intended. For the drug
product, this would classify as a new
drug product so the guidance would
apply to any new or higher levels of
degradation products.

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29
APPENDIX 2: CASE EXAMPLES
TO ILLUSTRATE POTENTIAL CONTROL APPROACHES
Case 1: Example of an Option 3 Control Strategy
An intermediate X is formed two steps away from the drug substance, and impurity A is
routinely detected in intermediate X. The impurity A is a stable compound and carries over to
the drug substance. A spike study of the impurity A at different concentration levels in
intermediate X was performed at laboratory scale. As a result of these studies, impurity A
was consistently removed to less than 30 percent of the threshold of toxicological concern
(TTC) based limit in the drug substance even when impurity A was present at 1 percent in
intermediate X. Because this intermediate X is formed only two steps away from the drug
substance and the impurity A level in the intermediate X is relatively high, the purging ability
of the process has additionally been confirmed by determination of impurity A in the drug
substance in multiple pilot scale batches and results were below 30 percent of the TTC-based
limit. Therefore, control of the impurity A in the intermediate X with an acceptance limit of 1
percent is justified and no test is warranted for this impurity in the drug substance
specification.
Case 2: Example of an Option 3 Control Strategy: Based on Predicted Purge From a
Spiking Study Using Standard Analytical Methods
A starting material Y is introduced in step 3 of a five-step synthesis, and an impurity B is
routinely detected in the starting material Y at less than 0.1 percent using standard analytical
methods. To determine if the 0.1 percent specification in the starting material is acceptable, a
purge study was conducted at laboratory scale where impurity B was spiked into starting
material Y with different concentration levels up to 10 percent and a purge factor of greater
than 500-fold was determined across the final three processing steps. This purge factor
applied to a 0.1 percent specification in starting material Y would result in a predicted level
of impurity B in the drug substance of less than 2 parts per million (ppm). Because this is
below the TTC-based limit of 50 ppm for this impurity in the drug substance, the 0.1 percent
specification of impurity B in starting material Y is justified without the need for providing
drug substance batch data on pilot scale or commercial scale batches.
Case 3: Example of an Option 2 and Option 4 Control Strategy: Control of Structurally
Similar Mutagenic Impurities
The step 1 intermediate of a five-step synthesis is a nitroaromatic compound that may contain
low levels of impurity C, a positional isomer of the step 1 intermediate and also a
nitroaromatic compound. The amount of impurity C in the step 1 intermediate has not been
detected by ordinary analytical methods, but it may be present at lower levels. The step 1
intermediate is positive in the bacterial mutagenicity assay. The step 2 hydrogenation reaction
results in a 99 percent conversion of the step 1 intermediate to the corresponding aromatic
amine. This is confirmed via in-process testing. An assessment of purge of the remaining step
1 nitroaromatic intermediate was conducted and a high purge factor was predicted based on
purge points in the subsequent step 3 and step 4 processing steps. Purge across the step 5
processing step is not expected and a specification for the step 1 intermediate at the TTC-
based limit was established at the step 4 intermediate (Option 2 control approach). The
positional isomer impurity C would be expected to purge via the same purge points as the
step 1 intermediate and, therefore, will always be much lower than the step 1 intermediate

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itself, and therefore, no testing is required, and an Option 4 control strategy for impurity C
can be supported without the need for any additional laboratory or pilot scale data.
Case 4: Example of an Option 4 Control Strategy: Highly Reactive Impurity
Thionyl chloride is a highly reactive compound that is mutagenic. This reagent is introduced
in step 1 of a five-step synthesis. At multiple points in the synthesis, significant amounts of
water are used. Because thionyl chloride reacts instantaneously with water, there is no chance
of any residual thionyl chloride to be present in the drug substance. An Option 4 control
approach is suitable without the need for any laboratory or pilot scale data.
Implementation of Guidance:
Implementation of the International Council for Harmonisation (ICH) guidance for industry
M7(R2) Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals
to Limit Potential Carcinogenic Risk (ICH M7(R2)) is encouraged after publication;
however, because of the complexity of the guidance, application of ICH M7(R2) is not
expected prior to 18 months after ICH publication.
The following exceptions to the 18-month timeline apply.
1. 	Ames tests should be conducted according to ICH M7(R2) upon ICH publication.
However, Ames tests conducted prior to publication of ICH M7(R2) need not be
repeated.
2. 	When development programs have started phase 2b/3 clinical trials prior to
publication of ICH M7(R2) these programs can be completed up to and including
marketing application submission and approval, with the following exceptions to ICH
M7(R2).
 No need for two (quantitative) structure-activity relationship assessments as
outlined in section VI (6) of ICH M7(R2).
 No need to comply with the scope of product impurity assessment as outlined in
section V (5) of ICH M7(R2).
 No need to comply with the documentation recommendations as outlined in
section IX (9) of ICH M7(R2).
3. 	Given the similar challenges for development of a commercial manufacturing process,
application of the aspects of ICH M7(R2) listed above to new marketing applications
that do not include phase 2b/3 clinical trials would not be expected until 36 months
after ICH publication of ICH M7(R2).

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31
APPENDIX 3: LIST OF COMPOUNDS IN ICH M7(R2) ADDENDUM:1
ACCEPTABLE INTAKES OR PERMISSIBLE DAILY EXPOSURES
Compound 	CAS# 	Chemical
Structure
AI 	or 	PDE
(μg/day)
Comment
Linear Extrapolation From TD50
Acrylonitrile 	107-13-1 	6 	TD50 linear
extrapolation
Benzyl chloride 	100-44-7 	41 	TD50 linear
extrapolation
Bis(chloromethyl)ether 	542-88-1 	0.004 	TD50 linear
extrapolation
1-Chloro-4-
nitrobenzene
100-00-5 	117 	TD50 linear
extrapolation
p-Cresidine 	120-71-8 	45 	TD50 linear
extrapolation
1,2-Dibromoethane 	106-93-4 	2 	TD50 linear
extrapolation
Dimethylcarbamyl
chloride
79-44-7 	0.6 (inhalation)*
5 (all other
routes)
TD50 linear
extrapolation
Epichlorohydrin 	106-89-8 	3 	TD50 linear
extrapolation
Ethyl bromide 	74-96-4 	32 	TD50 linear
extrapolation
Ethyl chloride 	75-00-3 	1,810 	TD50 linear
extrapolation
Glycidol 	556-52-5 	4 	TD50 linear
extrapolation
Hydrazine 	302-01-2 	0.2 (inhalation)*
39 (all other
routes)
TD50 linear
extrapolation
Methyl Chloride 	74-87-3 	1,361 	TD50 linear
extrapolation
1 See the International Council for Harmonisation guidance for industry M7(R2) Addendum: Application of the
Principles of the ICH M7 Guidance to Calculation of Compound-Specific Acceptable Intakes (July 2023). We
update guidances periodically. To make sure you have the most recent version of a guidance, check the FDA
guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.

Contains Nonbinding Recommendations
32
Compound 	CAS# 	Chemical
Structure
AI 	or 	PDE
(μg/day)
Comment
Styrene 	100-42-5 	154 	TD50 linear
extrapolation
Threshold-based PDE
Aniline 	62-53-3 	720 	PDE based on
Aniline HCl 	142-04-1 	threshold mode of
action
(hemosiderosis)
Endogenous and/or Environmental Exposure
Acetaldehyde 	75-07-0 	2,000 (oral) *
185 (all other
routes)
Oral PDE is based
on average food
intake; all other
routes based on
TD50 linear
extrapolation from
an inhalation study
Formaldehyde 	50-00-0 	8,000 or 215
ppb, whichever
is lower
(inhalation) *
10,000 (all other
routes)
Inhalation route
based on TD50
linear extrapolation
or local irritation;
all other routes
based on average
food intake
Hydrogen peroxide 	7722-84-1 	68,000 or 0.5%,
whichever is
lower
68 mg/day is 1% of
estimated
endogenous
production
Vinyl acetate 	108-05-4 	2,000 (oral) *
758 (all other
routes)
Oral PDE is based
on average food
intake for
acetaldehyde; all
other routes based
on TD50 linear
extrapolation from
an inhalation study
Other Cases
p-Chloroaniline
p-Chloroaniline HCl
106-47-8
20265-96-7
34 	AI based on liver
tumors for which
mutagenic mode of
action cannot be
ruled out

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33
Compound 	CAS# 	Chemical
Structure
AI 	or 	PDE
(μg/day)
Comment
Dimethyl Sulfate 	77-78-1 	1.5 	Carcinogenicity
data available, but
inadequate to
derive AI. Default
to TTC
CAS = Chemical Abstracts Service; AI = acceptable intake; PDE = permissible daily exposure; μg = microgram;
TD50 = 50 percent tumor incidence; ppb = parts per billion; mg = milligram; TTC = threshold of toxicological
concern.
* Route-specific limit.