Chronic Hepatitis B Virus Infection: Developing Drugs for Treatment

Administrative guidance, not enacted legislation. This captured publisher edition preserves the listed document and attachments; later developments are not independently consolidated.

Chronic HepaƟƟs B
Virus InfecƟon:
Developing Drugs for
Treatment
Guidance for Industry

U.S. Department of Health and Human Services
Food and Drug AdministraƟon
Center for Drug EvaluaƟon and Research (CDER)
April 2022
Clinical/AnƟmicrobial

Chronic HepaƟƟs B
Virus InfecƟon:
Developing Drugs for
Treatment
Guidance for Industry
AddiƟonal copies are available from:
Office of CommunicaƟons, Division of Drug InformaƟon
Center for Drug EvaluaƟon and Research
Food and Drug AdministraƟon
10001 New Hampshire Ave., Hillandale Bldg., 4th Floor
Silver Spring, MD 20993-0002
Phone: 855-543-3784 or 301-796-3400; Fax: 301-431-6353
Email: druginfo@fda.hhs.gov
hƩps://www.fda.gov/drugs/guidance-compliance-regulatory-informaƟon/guidances-drugs

U.S. Department of Health and Human Services
Food and Drug AdministraƟon
Center for Drug EvaluaƟon and Research (CDER)
April 2022
Clinical/AnƟmicrobial

TABLE OF CONTENTS
I. 	INTRODUCTION ......................................................................................................................1
II. 	BACKGROUND ........................................................................................................................2
III. 	DEVELOPMENT PROGRAM ......................................................................................................3
A. 	General Drug Development ConsideraƟons.............................................................................3
1. Early Phase Development ConsideraƟons ...................................................................................... 4
a. 	Pharmacology/toxicology development consideraƟons ......................................................... 4
b. 	Nonclinical virology development consideraƟons .................................................................. 6
c. 	Clinical pharmacology consideraƟons ..................................................................................... 9
2. Drug Development PopulaƟon ....................................................................................................... 9
3. Safety ConsideraƟons ................................................................................................................... 11
B. 	Phase 3 Efficacy Trial ConsideraƟons ..................................................................................... 12
1. Trial Design................................................................................................................................... 12
a. 	Chronic suppressive therapy ................................................................................................. 12
b. 	Finite duraƟon therapy ......................................................................................................... 13
2. Trial PopulaƟon ............................................................................................................................ 15
3. Entry Criteria ................................................................................................................................ 15
4. RandomizaƟon, StraƟficaƟon, and Blinding ................................................................................ 16
5. Specific PopulaƟons ..................................................................................................................... 16
a. 	PaƟents with HBV/HIV-1 coinfecƟon ..................................................................................... 16
b. 	PaƟents with HBV/HDV coinfecƟon ...................................................................................... 16
c. 	Pediatric paƟents .................................................................................................................. 17
6. Dose SelecƟon .............................................................................................................................. 19
7. Efficacy Endpoints ........................................................................................................................ 19
8. Trial Procedures and Timing of Assessments ............................................................................... 21
9. StaƟsƟcal ConsideraƟons ............................................................................................................. 21
a. 	Analysis populaƟons.............................................................................................................. 22
b. 	Efficacy analyses .................................................................................................................... 23
c. 	Handling missing data ........................................................................................................... 23
10. 	Accelerated Approval (Subpart H/I) ConsideraƟons ................................................................ 23
11. 	Benefit-Risk ConsideraƟons ..................................................................................................... 24

C. 	Other ConsideraƟons ............................................................................................................ 24
1. Clinical Virology ConsideraƟons ................................................................................................... 24
2. PharmacokineƟc/Pharmacodynamic ConsideraƟons .................................................................. 27
3. Labeling ConsideraƟons ............................................................................................................... 28
GLOSSARY OF ACRONYMS ................................................................................................................. 29
REFERENCES...................................................................................................................................... 30

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Chronic HepaƟƟs B Virus InfecƟon:
Developing Drugs for Treatment
Guidance for Industry1
This guidance represents the current thinking of the Food and Drug AdministraƟon (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 alternaƟve approach if it saƟsfies the requirements of the applicable statutes and regulaƟons.
To discuss an alternaƟve approach, contact the FDA office responsible for this guidance as listed on the
Ɵtle page.
I. 	INTRODUCTION
The purpose of this guidance is to assist sponsors in the clinical development of drugs and biologics for
the treatment of chronic hepaƟƟs B virus (HBV) infecƟon from the iniƟal invesƟgaƟonal new drug
applicaƟon (IND) through the new drug applicaƟon (NDA)/biologics license applicaƟon (BLA) and
postmarkeƟng phases. 2 Sponsors are also encouraged to communicate with the Division of AnƟvirals
through the pre-IND consultaƟon program to obtain advice in the development of drugs with unique
consideraƟons based on mechanism of acƟon, novel treatment approaches, or the use of novel
biomarkers. 3
This guidance does not address development of vaccines or blood-derived products, which are regulated
by the Center for Biologics EvaluaƟon and Research. This guidance also does not discuss general issues
of staƟsƟcal analysis or clinical trial design. Those topics are addressed in the ICH guidances for industry
1 This guidance has been prepared by the Division of Antivirals in the Center for Drug Evaluation and Research at
the Food and Drug Administration.
2 For the purposes of this guidance, all references to drugs include both human drugs and therapeutic biological
products unless otherwise specified.
3 See the Division of Antivirals Pre-IND Letter of Instruction web page at https://www.fda.gov/drugs/pre-ind-
consultation-program/division-anti-viral-dav-pre-ind-letter-instruction.

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E9 StaƟsƟcal Principles for Clinical Trials (September 1998) and E10 Choice of Control Group and Related
Issues in Clinical Trials (May 2001), respecƟvely. 4
The contents of this document do not have the force and effect of law and are not meant to bind the
public in any way, unless specifically incorporated into a contract. This document is intended only to
provide clarity to the public regarding exisƟng requirements under the law. FDA guidance documents,
including this guidance, should be viewed only as recommendaƟons, unless specific regulatory or
statutory requirements are cited. The use of the word should in Agency guidances means that
something is suggested or recommended, but not required.
II. 	BACKGROUND
HBV is an enveloped DNA virus belonging to the Hepadnavirus family. The highly stable covalently
closed circular viral DNA (cccDNA) funcƟons as a nonreplicaƟve minichromosome and persists
throughout the lifespan of infected hepatocytes. The cccDNA is not eliminated by currently approved
therapies that include drugs from the nucleoside/nucleoƟde reverse transcriptase inhibitor (NrtI) class,
and pegylated interferon.
Chronic HBV (CHB) infecƟon results in progressive liver disease ranging from asymptomaƟc to severe
disease with complicaƟons including cirrhosis, liver failure, and the development of hepatocellular
carcinoma (HCC). In untreated adults with CHB, the cumulaƟve 5-year incidence of cirrhosis is 8 to 20
percent; and among those with cirrhosis, the 5-year cumulaƟve risk of hepaƟc decompensaƟon is 20
percent, and risk of HCC is 2 to 5 percent (Terrault et al. 2016). An effecƟve vaccine and anƟviral
therapies are approved for the prevenƟon of HBV infecƟon and treatment of CHB, respecƟvely.
Currently available therapies achieve sustained suppression of HBV DNA while on treatment, but rates of
HBV surface anƟgen (HBsAg) loss with or without seroconversion to anƟ-HBsAg (HBsAb) remain low.
Sustained HBV DNA suppression is associated with serum alanine aminotransferase (ALT) normalizaƟon
and improvement in liver histology including regression of hepaƟc fibrosis and cirrhosis (Chang et al.
2010; Marcellin et al. 2013; BuƟ et al. 2015). EffecƟve anƟviral therapy for CHB reduces disease-related
complicaƟons, such as hepaƟc decompensaƟon and liver failure, and decreases risk of HCC (Lok et al.
2016; Papatheodoridis et al. 2017). Clearance of HBsAg is associated with reduced risk of hepaƟc
decompensaƟon and improved survival (Terrault et al. 2016). HBsAg loss is considered the best
predictor of sustained remission off-treatment (Terrault et al. 2016). New finite duraƟon therapies target
4 We update guidances periodically. For 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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treatment regimens that can achieve sustained suppression of HBV DNA off-treatment with HBsAg loss
(with or without HBsAb seroconversion) with low risk of virologic relapse (as defined by HBV DNA) and
minimal risk of liver disease progression aŌer the treatment is stopped (Lok et al. 2017).
III. 	DEVELOPMENT PROGRAM
A. 	General Drug Development ConsideraƟons
This secƟon discusses nonclinical and early phase clinical development consideraƟons, followed by
issues related to the target populaƟon for drug development, assessment of acƟvity in early phase trials,
and safety consideraƟons.

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1. 	Early Phase Development ConsideraƟons
Early clinical evaluaƟon should provide sufficient data to establish safety and evidence of anƟviral acƟvity
to support the phase 3 trials.
a. 	Pharmacology/toxicology development consideraƟons
Pharmacology/toxicology development consideraƟons for single invesƟgaƟonal drugs intended to treat
CHB should follow the approaches outlined in exisƟng guidances for drug development. 5
When a combinaƟon of two or more early stage invesƟgaƟonal drugs to treat CHB is being developed,
sponsors should discuss with the FDA whether combinaƟon toxicology studies are needed (including the
design of such studies) to support clinical trials for the intended combinaƟon. When combinaƟon
toxicology studies are conducted, usually no more than two drugs should be tested simultaneously in a
parƟcular arm of a toxicology study. Nonclinical combinaƟon studies of an invesƟgaƟonal drug plus an
approved drug or licensed biological product generally are not needed unless data from nonclinical
studies of an invesƟgaƟonal drug suggest a potenƟal for serious synergisƟc toxicity with an approved
drug or licensed biological product.
In general, sponsors developing drugs intended to treat CHB with proposed treatment duraƟons of 6
months or more should conduct carcinogenicity studies. 6 Sponsors should submit carcinogenicity
studies with an iniƟal NDA. However, under limited circumstances and with prior wriƩen agreement, the
FDA may consider allowing sponsors to submit the completed carcinogenicity studies during the
postmarkeƟng period under secƟon 505(o)(3) of the Federal Food, Drug, and CosmeƟc Act (FD&C Act) 7
,
as long as the studies have been iniƟated before NDA submission.
5 See the ICH guidances for industry M3(R2) Nonclinical Safety Studies for the Conduct of Human Clinical Trials
and Marketing Authorization for Pharmaceuticals (January 2010) and S6(R1) Preclinical Safety Evaluation of
Biotechnology-Derived Pharmaceuticals (May 2012).
6 See the ICH guidance for industry S1A The Need for Long-Term Rodent Carcinogenicity Studies of
Pharmaceuticals (March 1996).
7 See also the draft guidance for industry Postmarketing Studies and Clinical Trials—Implementation of Section
505(o)(3) of the Federal Food, Drug, and Cosmetic Act (October 2019). When final, this guidance will represent
the FDA’s current thinking on this topic. For 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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Sponsors developing biological products should follow approaches outlined in ICH S6(R1) and discuss
their proposals for a carcinogenicity risk assessment with the FDA during clinical development to
facilitate a final assessment needed to support a BLA.

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b. 	Nonclinical virology development consideraƟons
Sponsors should consider recommendaƟons for general anƟviral drug development in the draŌ guidance
for industry AnƟviral Product Development—ConducƟng and Submiƫng Virology Studies to the Agency
(February 2014).8 The FDA encourages detailed study reports describing the mechanism of acƟon,
anƟviral acƟvity in cell culture, cytotoxicity, and mitochondrial toxicity (Marroquin et al. 2007; Arnold et
al. 2012), animal models,9 and resistance studies. AddiƟonally, sponsors are advised to provide the
following nonclinical virology data for invesƟgaƟonal drugs developed specifically for the treatment of
CHB.
Resistance and cross-resistance
HBV is differenƟated into 10 genotypes (A through J) with many different subtypes. Drugs targeƟng viral
proteins or sequence targets will likely be impacted by genotype- and subtype-specific variaƟons that
occur in the drug target as well as variaƟons that evolve in the presence of the drug that allow the virus
to develop resistance. Therefore, characterizing resistance pathways and their relaƟonship to HBV
genomic variaƟons helps idenƟfy subjects who will benefit from the drug and also helps idenƟfy
potenƟal cross-resistance with other drugs having a similar mechanism of acƟon.
HBV does not generally grow well enough in cell culture to select for resistant virus in the presence of
drug. When possible, we recommend that resistance assessments be performed for all animal studies
that assess the anƟviral acƟvity of an invesƟgaƟonal drug in infected animals receiving the drug that
experience viral breakthrough. In addiƟon, a resistance monitoring plan for idenƟfying changes in viral
targets associated with treatment failure should be included in the protocols or can be submiƩed
separately for each clinical trial that will treat subjects with CHB.
 	Amino acid subsƟtuƟons or nucleoƟde mutaƟons associated with the development of resistance
(i.e., changes from baseline) to an invesƟgaƟonal drug should be determined by sequencing the
drug target and validated by introducing resistance-associated subsƟtuƟons or mutaƟons into
the HBV reference genome using site-directed mutagenesis and determining the fold-shiŌ in
8 When final, this guidance will represent the FDA’s current thinking on this topic.
9 We support the principles of the 3Rs (reduce/refine/replace) for animal use in tesƟng when feasible. FDA
encourages sponsors to consult with review divisions when considering a nonanimal tesƟng method believed to be
suitable, adequate, validated, and feasible. FDA will consider if the alternaƟve method could be assessed for
equivalency to an animal test method.

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suscepƟbility. Results from these studies help idenƟfy resistance pathways and support the
drug’s proposed mechanism of acƟon. Lack of a shiŌ in suscepƟbility does not exclude a
resistance associaƟon for a specific subsƟtuƟon or mutaƟon that occurs in two or more
independent events.
Cross-resistance should be assessed to determine if resistance against approved HBV drugs with the
same target confers resistance to the drug being developed and vice versa. The development of cross-
resistance to epitopes of approved HBV vaccines should be assessed.
ConsideraƟons for oligonucleoƟde-based invesƟgaƟonal drugs
Knockdown of viral protein expression via oligonucleoƟde-based therapeuƟcs is an acƟve area for the
development of anƟviral drugs. These drugs, which have a nucleic acid target, present potenƟal off-
target binding at mismatched sequences that could lead to species-specific toxiciƟes not necessarily
detected in toxicology studies. Therefore, we recommend that sequence-dependent off-target
assessments be conducted for such drugs using appropriate in silico and in vitro methodologies to
idenƟfy potenƟal off-target mismatches that can be invesƟgated and potenƟally monitored during
clinical development. The Division recognizes that many addiƟonal factors, such as temporal and cell
type specific expression, pharmacokineƟc (PK) properƟes, and hybridizaƟon-dependent efficiencies may
be considered in the overall risk assessment of potenƟal off-target effects (refer to Lindow et al. 2012 for
a general approach). The following points should be considered when designing sequence-dependent
off-target assessments:
 	Several different classes of oligonucleoƟde-based therapeuƟcs (small interfering RNAs and
anƟsense oligonucleoƟdes, etc.) exist. The criteria for defining high-risk off-target mismatches
are expected to differ for each class; appropriate criteria should be provided and jusƟfied for
each drug.
 	All elements of the oligonucleoƟde drug product that are potenƟally available for mismatch
binding should be assessed, including both the sense and anƟsense strands, overlapping ends,
etc.
 	There are mulƟple in silico approaches that may be considered, and we recommend sponsors
jusƟfy the methods and approaches used. In silico studies can be used to do the following:

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– 	IdenƟfy all potenƟal off-target mismatches, regardless of Ɵssue expression, in the human
transcriptome, including the mitochondrial transcriptome; for each of these, describe
available informaƟon on mouse knockouts and human geneƟc diseases. Sponsors should
specify and jusƟfy the criteria for defining a potenƟal off-target mismatch.
– 	Determine whether each off-target site in the human transcriptome is conserved in the
animal species in which anƟviral assessments and pivotal toxicology studies are performed.
– 	Determine the variaƟon within the off-target mismatches in the transcriptomes of different
ethnic populaƟons in the United States, when feasible, to assess whether certain
populaƟons may be more suscepƟble to off-target effects than others.
 	In vitro assessments of possible off-target binding (cell-based analysis, RNA-seq, etc.) should be
conducted to confirm or eliminate the importance of each off-target mismatch determined via in
silico assessments.
 	An overall risk assessment of potenƟal off-target effects should be provided along with the off-
target assessment data.
ConsideraƟons for drugs developed to modulate innate and adapƟve immune responses
Drugs developed to modulate innate and adapƟve immune responses to chronic HBV infecƟon are likely
to target host factors and induce or repress immune biomarkers before having an impact on HBV
replicaƟon or clearance of HBV infected hepatocytes. Nonclinical studies should describe the specific
mechanism of acƟon of the drug and demonstrate that immune modulaƟon in cell culture and animal
models of HBV infecƟon results in suppression of HBV replicaƟon, as measured by HBV DNA or HBsAg
loss, or that the HBV cccDNA reservoir is reduced by assessing cccDNA levels. In addiƟon, given that
these drugs may target host factors, it is important to determine that the target of the drug is conserved,
having similar affinity between the animal species being assessed and the human target.
TargeƟng host factors
For drugs targeƟng host factors, polymorphisms in the gene encoding the target should be assessed to
determine whether the drug will be more effecƟve or less effecƟve in different populaƟons. Sponsors
should idenƟfy key racial and ethnic groups in the United States who will be part of the proposed

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indicaƟon at the iniƟaƟon of drug development. If a nonclinical assay to assess the drug effect is
available, mulƟple samples from each of these groups in the United States should be evaluated to
determine whether race or ethnicity may be a factor contribuƟng to efficacy (Forde et al. 2013).
Samples should be collected during clinical trials to determine the virus genotype of subjects who
respond less favorably to treatment.
c. 	Clinical pharmacology consideraƟons
In general, dose selecƟon for early efficacy trials should be predicted to provide plasma drug exposures
that exceed by severalfold the protein binding-adjusted, cell culture EC 50 value of the drug for the
relevant HBV genotype/subtype. In cases where either total (protein bound plus unbound) or free
(unbound) drug concentraƟons in plasma may not be related to anƟviral acƟvity, sponsors may provide
jusƟficaƟon for dose selecƟon based on drug concentraƟon in other relevant Ɵssues. The dose selecƟon
should also consider the safety data from the previous phase 1 trials and animal studies.
Sponsors should refer to the appropriate clinical pharmacology guidances for industry to inform the
need and design of drug-drug interacƟon studies and PK studies in paƟents with renal or hepaƟc
impairment. 10 We encourage sponsors to conduct these studies, if needed, early in development to
inform the management of drug interacƟons and the inclusion of paƟents with renal and hepaƟc
impairment in phase 3 trials as appropriate. See secƟon III. B. 6., Dose SelecƟon, for dose selecƟon for
phase 2 and 3 trials and secƟon III. C. 2.,
PharmacokineƟc/Pharmacodynamic ConsideraƟons, for other PK and pharmacodynamic consideraƟons.
2. 	Drug Development PopulaƟon
Therapies should be developed for use in a wide range of paƟents with CHB, including pediatric
populaƟons.
Early phase clinical trials should focus on the adult populaƟon without cirrhosis. IniƟal trials can be
conducted in HBV e anƟgen posiƟve (HBeAg-posiƟve) or HBV e anƟgen negaƟve (HBeAg-negaƟve)
10 See the guidance for industry Pharmacokinetics in Patients With Impaired Hepatic Function: Study Design, Data
Analysis, and Impact on Dosing and Labeling (May 2003). See also the guidances for industry Clinical Drug
Interaction Studies—Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions (January 2020), In
Vitro Drug Interaction Studies—Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions (January
2020), and the draft guidance for industry Pharmacokinetics in Patients With Impaired Renal Function—Study
Design, Data Analysis, and Impact on Dosing (September 2020). When final, this guidance will represent the
FDA’s current thinking on these topics.

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paƟents with acƟve disease who are treatment-naïve, or those who were previously treated but
currently viremic, off-treatment. Trials can also be conducted in HBeAg-posiƟve or HBeAg-negaƟve
paƟents who are virally suppressed on NrtIs. In addiƟon to endpoints discussed in secƟon III. B.,
sponsors can evaluate exploratory endpoints in early phase trials to gather data to inform and support
the choice of appropriate endpoints in late phase trials, parƟcularly those evaluaƟng treatments of finite
duraƟons. Some of these exploratory endpoints may include the following:
• 	Change in quanƟtaƟve HBsAg (qHBsAg) concentraƟon at various Ɵme points on treatment
• 	QuanƟtaƟve HBeAg levels
• 	QuanƟtaƟve HBV RNA levels
• 	QuanƟtaƟve HBV core-related anƟgen (HBcrAg) levels
• 	cccDNA quanƟficaƟon
• 	QuanƟtaƟve HBsAg levels from integrated HBV genome fragments
• 	QuanƟtaƟve HBsAg-anƟ-HBs immune complex levels
Also depending on the drug’s mechanism of acƟon, liver biopsy findings can be used in certain proof-of-
concept studies to further understand the effect of the drug on the cccDNA reservoir and/or to help
beƩer understand potenƟal surrogate markers of anƟviral acƟvity.
CHB is a global disease, and clinical trials are oŌen conducted in mulƟple countries. FDA will accept a
well-designed and well-conducted foreign clinical study not conducted under an IND as support for an
IND or applicaƟon for markeƟng approval if the trial was conducted in accordance with good clinical
pracƟce and if the FDA is able to validate the data from the trial through an onsite inspecƟon if the
Agency deems it necessary.11 When sponsors rely on foreign data, these should be supported with
informaƟon about predominant HBV genotypes and subtypes in the region or regions (Schweitzer et al.
2015). Development programs should include a sufficient number of U.S. paƟents to ensure prevalent
genotypes in the U.S. populaƟon are represented. FDA strongly encourages sponsors to provide a plan
to address inclusion of clinically relevant subpopulaƟons with regard to age, sex, race, and ethnicity in
the clinical trials to support an NDA or BLA, no later than the end-of-phase 2 meeƟng.12
11 See 21 CFR 312.120; 21 CFR 314.106.
12 See the guidance for industry CollecƟon of Race and Ethnicity Data in Clinical Trials (October 2016).

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3. 	Safety ConsideraƟons
In general, we recommend that iniƟal markeƟng applicaƟons for drugs intended to treat CHB contain a
total safety database of about 1,000 to 1,500 subjects exposed to the proposed dose and duraƟon of
treatment. Depending on the drug safety profile and concerns idenƟfied during the development
process, a larger database or long duraƟons of posƩreatment follow-up may be needed.
In addiƟon to rouƟne safety monitoring, the safety monitoring plans should consider the mechanism of
acƟon of the drug, as there may be different safety concerns associated with specific drugs both during
treatment and aŌer treatment cessaƟon. Some of the notable safety concerns associated with immune
modulatory therapies are immune-mediated hepaƟƟs flares and autoimmunity (e.g., immune-related
adverse events observed with checkpoint inhibitors). The specific criteria for defining and monitoring for
hepaƟƟs flares during treatment and aŌer stopping therapy should be prespecified in the clinical trial
protocols. The safety profile observed in early phase trials should guide the monitoring plan for late
phase trials.
Severe acute exacerbaƟons of HBV infecƟon may occur aŌer disconƟnuaƟon of anƟ-HBV therapy,
parƟcularly in the absence of HBsAg loss. Subjects should be monitored closely with both laboratory and
clinical follow-up aŌer disconƟnuaƟon of anƟ-HBV therapy. The duraƟon of follow-up should consider
the mechanism of acƟon and the half-life of the specific invesƟgaƟonal drug. In certain circumstances,
resumpƟon of anƟ-HBV therapy may be warranted. The detailed plan and criteria for treatment
reiniƟaƟon should be prespecified in the clinical trial protocols.
Clinical trial protocols should include predefined algorithms for data collecƟon in the seƫng of
significant hepaƟc events to ensure that the relevant data are available for further assessment and
adjudicaƟon of these cases to differenƟate between potenƟal eƟologies. The outcomes for all serious
hepaƟc events should be systemaƟcally evaluated during clinical development. EvaluaƟon by an
independent adjudicaƟon commiƩee is encouraged.
For a drug approved for use in paƟents without cirrhosis or with compensated cirrhosis, the database
needed to extend use to the decompensated cirrhoƟc populaƟon would depend on the safety profile of
the invesƟgaƟonal drug and the overall benefit-risk profile for the indicated populaƟon. Similarly,
obtaining safety data in other subpopulaƟons, such as in paƟents coinfected with hepaƟƟs D virus (HDV),
may be important for certain clinical development programs. We encourage sponsors to discuss with
the FDA safety-related consideraƟons, including but not limited to the size of the safety database, before
the iniƟaƟon of phase 3 trials.

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B. 	Phase 3 Efficacy Trial ConsideraƟons
Sponsors can submit an NDA/BLA to support markeƟng approval of a drug in a single paƟent populaƟon
(e.g., treatment-naïve paƟents or paƟents who are virally suppressed on NrtIs). Such an applicaƟon
should include at least two adequate and well-controlled trials conducted in the proposed populaƟon.
AlternaƟvely, sponsors can choose to pursue an indicaƟon for different populaƟons (e.g., a trial in
treatment-naïve subjects and a second trial in subjects who are virally suppressed on NrtIs). In these
situaƟons, the NDA/BLA should contain at least one adequate and well-controlled trial in each paƟent
populaƟon, with adequate supporƟng data.
1. 	Trial Design
Randomized controlled trials are recommended to establish efficacy because of the heterogeneity of the
natural course of CHB. Appropriate trial designs depend on whether the therapeuƟc is intended for
chronic suppressive therapy or therapy of finite duraƟon as discussed below.
a. 	Chronic suppressive therapy
Sponsors developing drugs for chronic suppressive therapy of CHB should consider the following trial
design opƟons:
 	A randomized controlled noninferiority (NI) (or superiority) trial comparing the invesƟgaƟonal
drug with an approved acƟve control arm—The primary efficacy endpoint should be
undetectable HBV DNA13 aŌer 48 weeks on-treatment in HBeAg-posiƟve subjects, HBeAg-
negaƟve subjects, or both. The acƟve comparator should be an anƟviral drug that is
recommended for treatment of CHB and reflects current pracƟce at the Ɵme of trial iniƟaƟon.
The paƟent populaƟon may be treatment-naïve or previously treated subjects with detectable
HBV DNA. PotenƟal concerns related to the development of resistance when evaluaƟng an
invesƟgaƟonal drug with a low barrier to resistance as a monotherapy should be addressed. For
an NI design, determinaƟon of the NI margin should be discussed with the FDA.
13 Defined as less than the lower limit of quanƟficaƟon (LLOQ), specifying if the results are target detected (TD) or
target not detected (TND).

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13
 	A randomized controlled add-on superiority trial comparing an invesƟgaƟonal drug plus an
approved NrtI with an NrtI alone—However, for this trial design, it is not clear what the most
appropriate primary endpoint should be to demonstrate the invesƟgaƟonal drug’s clinical
contribuƟon. Presently, HBV DNA is not recommended as a primary endpoint for an add-on trial
because it is unclear what incremental numerical benefits in HBV DNA, over the substanƟal HBV
DNA suppression achieved by an NrtI alone, are predicƟve of clinical benefit. Other endpoints
such as HBsAg clearance or another surrogate found to be predicƟve of clinical benefit may be
considered; however, the trial design and endpoints should be discussed with the FDA in
advance of trial iniƟaƟon.
b. 	Finite duraƟon therapy
The appropriate trial design depends on the paƟent populaƟon being studied and the treatment
regimen being evaluated. See secƟon III. B. 7., Efficacy Endpoints for a descripƟon of efficacy endpoints
that could be used for evaluaƟon of finite duraƟon therapies in clinical trials.
Sponsors developing drugs for finite duraƟon therapy of CHB should consider the following trial design
opƟons:
Virally suppressed on NrtIs
To evaluate the primary efficacy outcome of sustained HBV DNA suppression off-treatment with HBsAg
loss in subjects with acƟve disease (HBeAg-posiƟve or HBeAg-negaƟve CHB) who are virally suppressed
on NrtIs, sponsors can consider an add-on superiority trial against placebo with a current NrtI treatment
regimen as the background therapy. The co-primary efficacy endpoints14 of HBsAg loss and sustained
HBV DNA suppression should be assessed at the 6-month posƩreatment Ɵme point with addiƟonal
follow-up to monitor for durability of response (i.e., sustained HBV DNA suppression and HBsAg loss) off-
treatment. In general, off-treatment refers to disconƟnuaƟon of all therapies (i.e., invesƟgaƟonal agent
and background NrtI regimen). To demonstrate sustained response off-treatment, sponsors should
systemaƟcally assess the duraƟon of a treatment consolidaƟon period, defined as the duraƟon of
conƟnued treatment needed aŌer achieving HBsAg loss, during late phase trials. This may vary based on
the mechanism of acƟon and half-life of the specific invesƟgaƟonal drug.
14 See draŌ guidance for industry MulƟple Endpoints in Clinical Trials (January 2017). When final, this guidance will
represent the FDA’s current thinking on this topic.

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14
Sponsors should use the following criteria for stopping NrtI therapy at the end of the invesƟgaƟonal
treatment period when evaluaƟng a finite duraƟon therapy: (1) applied equally across treatment arms,
as applicable; (2) well-defined in the protocol; and (3) stringent, such as HBsAg loss or substanƟal HBsAg
decline or marked reducƟon in other important biomarkers idenƟfied in phase 2 trials. It is expected
that few subjects would meet such criteria on the placebo arm. The criteria for stopping NrtI therapy
should be based on clinical evidence that also reflects current pracƟce guidelines recommended by the
authoritaƟve scienƟfic bodies to ensure that the disconƟnuaƟon of NrtI therapy does not pose undue
safety risk to the trial parƟcipants. Sponsors should discuss with the FDA the use of biomarkers as a
trigger for treatment interrupƟon in advance of trial iniƟaƟon.
AlternaƟvely, an outcome of sustained HBV DNA suppression off-treatment without HBsAg clearance can
be evaluated aŌer a finite treatment duraƟon using a superiority trial design comparing the
invesƟgaƟonal drug plus an NrtI with an NrtI alone.
Treatment-naïve
An outcome of sustained HBV DNA suppression off-treatment with HBsAg loss can be evaluated in
treatment-naïve subjects by demonstraƟng superiority to an acƟve control, or, in paƟents in whom
treatment is currently not indicated per treatment guidelines, superiority to placebo. In certain paƟent
populaƟons (e.g., for paƟents in the immune-tolerant phase with mild necroinflammaƟon or fibrosis)
comparison with placebo may be feasible as current treatment guidelines do not recommend treatment
for these paƟents. In some of the trial design scenarios, subjects in the placebo group may be rolled
over to an acƟve invesƟgaƟonal drug before the compleƟon of the trial based on a prespecified interim
analysis. Sponsors should prospecƟvely plan these analyses15 and should discuss with the FDA before
trial enrollment.
Sponsors considering an NI trial design should discuss in advance with the FDA their trial designs and
jusƟficaƟons of the proposed NI margin based on historical evidence of treatment effect of the acƟve
control. In general, the acƟve comparator in an NI trial should be an FDA-approved drug that is
considered the standard of care for the specific indicaƟon and populaƟon being studied. A detailed
protocol and staƟsƟcal analysis plan (SAP) should be submiƩed for review.
15 See the guidance for industry AdapƟve Designs for Clinical Trials of Drugs and Biologics (November 2019).

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15
2. 	Trial PopulaƟon
PaƟents fulfilling one of the following two criteria for CHB should be enrolled (Centers for Disease
Control and PrevenƟon 2012):
(1) NegaƟve immunoglobulin M (IgM) anƟbodies to HBV core anƟgen and a posiƟve result on one of
the following tests: HBsAg, HBeAg, or nucleic acid test for hepaƟƟs B virus DNA (including
qualitaƟve, quanƟtaƟve, and genotype tesƟng); or
(2) PosiƟve HBsAg result or posiƟve nucleic acid test for HBV DNA (including qualitaƟve,
quanƟtaƟve, and genotype tesƟng) or posiƟve HBeAg on two occasions at least 6 months apart
(any combinaƟon of these tests performed 6 months apart is acceptable).
Sponsors should consider evaluaƟng drug efficacy in key CHB subpopulaƟons, including but not
limited to the following:
• 	HBeAg-posiƟve and HBeAg-negaƟve subjects
• 	Subjects with cirrhosis
• 	Subjects with decompensated liver disease
3. 	Entry Criteria
The presence or absence of cirrhosis at study entry should be documented based on clinical assessment
or previous liver biopsy, when available. As the criteria for diagnosing cirrhosis using noninvasive
methods are not yet well defined, parƟcularly in paƟents who are virally suppressed, the use of a
noninvasive modality to define presence or absence of cirrhosis in a trial protocol should be supported
by references that summarize performance characterisƟcs and sensiƟvity and specificity of the modality
for idenƟfying paƟents with cirrhosis.

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4. 	RandomizaƟon, StraƟficaƟon, and Blinding
Sponsors should conduct randomized, double-blind trials whenever feasible to reduce the likelihood of
potenƟal biases. In general, trials should be designed to evaluate the effect of invesƟgaƟonal therapies
in subjects with key disease characterisƟcs. PaƟent subpopulaƟons could be evaluated in separate trials
or as separate strata in a single trial. If mulƟple paƟent populaƟons are included in a single trial,
sponsors should consider straƟfying groups at randomizaƟon based on baseline variables (e.g., HBeAg
status, HBsAg level, presence or absence of cirrhosis, and HBV DNA level) and ensure that an adequate
number of subjects are in each stratum to provide informaƟve data.
5. 	Specific PopulaƟons
a. 	PaƟents with HBV/HIV-1 coinfecƟon
The overall treatment goals for paƟents with HBV/HIV coinfecƟon remain idenƟcal to those described for
the HBV-monoinfected populaƟon. Sponsors should consider including subjects coinfected with HIV in
the clinical trials evaluaƟng finite duraƟon HBV therapies. In cases where there is a strong raƟonale for
exclusion of paƟents with HBV/HIV coinfecƟon, the raƟonale should be addressed in the trial protocol.
The concurrent use of HIV anƟretroviral drugs that are also effecƟve against HBV (e.g., HIV
nucleoside/nucleoƟde reverse transcriptase inhibitors) may have implicaƟons for treatment cessaƟon
when evaluaƟng finite duraƟon HBV therapies and possibly confound interpretaƟon of efficacy outcome
as subjects conƟnue their HIV nucleoside/nucleoƟde reverse transcriptase inhibitor -based anƟretroviral
regimen. Because of the various interacƟons between HIV and HBV therapies, we recommend sponsors
discuss their plans with and obtain feedback from the FDA.
b. 	PaƟents with HBV/HDV coinfecƟon
InfecƟon with HDV only occurs in the seƫng of concurrent HBV infecƟon (Wranke and Wedemeyer
2016). According to the World Health OrganizaƟon, an esƟmated 15 million to 20 million people
worldwide are living with HBV/HDV coinfecƟon (World Health OrganizaƟon 2017). A meta-analysis
reported a much higher worldwide HBV/HDV coinfecƟon prevalence of 62 million to 72 million (Chen et
al. 2019). RelaƟve to HBV monoinfecƟon, HBV/HDV coinfecƟon leads to more severe liver disease
resulƟng in a greater risk of cirrhosis, HCC, and hepaƟc decompensaƟon/failure.
The ulƟmate goal of treatment in paƟents with HBV/HDV coinfecƟon is clearance or long-term
suppression of both viruses. CHB treatment leading to loss of HBsAg may ulƟmately lead to the
clearance of HDV infecƟon (Wranke and Wedemeyer 2016). HDV superinfecƟon frequently leads to
spontaneous suppression of HBV (Huang and Lo 2014), and the effect of specific HBV therapies on the

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17
interplay between the two viruses cannot be predicted. The possibility of HBV reacƟvaƟon needs to be
considered when HDV is suppressed aŌer HDV treatment iniƟaƟon. To miƟgate the risk of HBV
reacƟvaƟon and associated hepaƟƟs flares, it is preferred to have paƟents on NrtI suppressive therapy
before they receive HDV treatment. RecommendaƟons for trials in paƟents with HBV/HDV coinfecƟon
are beyond the scope of this guidance and are included in a separate draŌ guidance.16 Sponsors should
discuss development plans directly with the FDA.
c. 	Pediatric paƟents
Pediatric assessments are required under secƟon 505B of the FD&C Act as part of the overall drug
development program for a “new acƟve ingredient, new indicaƟon, new dosage form, new dosing
regimen, or new route of administraƟon,” 17 unless those assessments are waived. 18 Sponsors should
discuss their plans for pediatric assessments with the review division and be aware of Ɵming and content
requirements for pediatric study plans under secƟon 505B(e) of the FD&C Act. Sponsors are required to
submit pediatric study plans no later than 60 days aŌer an end-of-phase 2 meeƟng or such other Ɵme as
may be agreed upon by the FDA and the sponsor. 19 Because progressive liver disease is uncommon in
young children with HBV infecƟon, it is generally not recommended to include paƟents younger than 2
years of age in most development programs. Further, treatment generally is not recommended in
children younger than 2 years of age, as per current treatment guidelines (Terrault et al. 2016).
In general, pediatric clinical trials can be iniƟated aŌer phase 2 adult data characterizing the safety
profile and preliminary evidence of efficacy are available. Given the natural history of CHB infecƟon, the
dynamic relaƟonship between viral replicaƟon and the host immune response in pediatric paƟents may
differ from that observed in adults, hence extrapolaƟon of efficacy may not be possible in all scenarios
and could be considered on a case-by-case basis depending on the mechanism of acƟon of the
invesƟgaƟonal drug or drugs and the pediatric age group being evaluated.
16 See the draŌ guidance for industry Chronic HepaƟƟs D Virus InfecƟon: Developing Drugs for Treatment
(November 2019). When final, this guidance will represent the FDA’s current thinking on this topic.
17 See section 505B(a)(1)(A) of the FD&C Act; 21 U.S.C. 355c(a)(1)(A).
18 See section 505B(a)(5) of the FD&C Act.
19 See section 505B(e)(2)(A)(ii) of the FD&C Act; see also the guidance for industry Pediatric Study Plans:
Content of and Process for Submitting Initial Pediatric Study Plans and Amended Initial Pediatric Study Plans (July
2020).

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18
In cases in which extrapolaƟon of efficacy from adults to pediatrics is possible, aŌer criƟcal PK
parameters of a drug are idenƟfied in adults, pediatric development programs can focus on idenƟfying
dosing regimen(s) that achieve pediatric exposures similar to adults to demonstrate effecƟveness in
pediatric populaƟons in which treatment is indicated as per current treatment guidelines. AddiƟonal
clinical data should be obtained to assess whether anƟviral acƟvity is comparable to that observed in
adult trials. Early discussion with the FDA on the appropriate endpoints and pediatric trial design is
encouraged.
In the absence of a serious safety signal in adults, sponsors should enroll adolescents20 in phase 3 adult
trials or conduct a dedicated adolescent trial concurrently with the phase 3 adult trials. Confirmatory
PK, safety, and efficacy data from this age group should be included as part of the data included at the
Ɵme of filing of the original NDA/BLA.21
Typically, the nonadolescent pediatric populaƟon (for the purpose of this guidance, 2 to younger than 12
years of age) is divided into several groups or cohorts according to age or weight for enrollment into
trials. Weight, rather than age, is the preferred criterion for enrollment because dosing
recommendaƟons for most anƟviral drugs are weight-based. In addiƟon, within clinical studies, sponsors
should enroll the cohorts in parallel rather than in series, unless a drug has a specific safety or drug
disposiƟon factor that warrants a different approach. Dose selecƟon for pediatric treatment trials (e.g.,
phase 2 or 3) should be supported by PK data generated from the iniƟal PK/safety phase of the pediatric
study and results of available modeling and simulaƟon. Sponsors should discuss the dose selecƟon with
the FDA before iniƟaƟng the phase 2 or 3 pediatric trials.
The pediatric trials should also obtain data to support safety in pediatric populaƟons. In general, a safety
database of about 100 subjects receiving the proposed dose and treatment duraƟon is recommended.
The parƟcipants should be adequately distributed across the pediatric age group for which studies are
required. Long-term follow-up data should be collected from pediatric trials to assess long-term safety
as well as durability of treatment response. If clinical trials in adults have demonstrated differences in
safety profile or dosing based on fibrosis stage, pediatric subjects should be assessed for presence or
absence of cirrhosis using the most appropriate modality for each study locaƟon.
20 For the purpose of this guidance, adolescents are defined as age 12 to younger than 18 years of age.
21 We note that, for applicaƟons to which secƟon 505B applies, all pediatric assessments must be submiƩed with
the applicaƟon unless those assessments have been deferred (secƟon 505B(a)(1)(A)).

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SecƟon 505B of the FD&C Act also mandates that the requisite pediatric assessments be conducted
using a formulaƟon of the drug that is appropriate for each pediatric group being studied.22 Adult
formulaƟons generally are considered appropriate for adolescent paƟents (Momper et al. 2013), but
younger paƟents, who may not be able to swallow pills, may require different formulaƟons. Therefore,
pediatric formulaƟon development should begin as early as possible to enable the development of
appropriate pediatric formulaƟons of invesƟgaƟonal drugs.
6. 	Dose SelecƟon
The results from proof-of-concept anƟviral acƟvity trials can be used to guide the selecƟon of doses to
be evaluated in subsequent trials. Sponsors are encouraged to use various quanƟtaƟve clinical
pharmacology approaches that leverage the totality of available informaƟon on exposure and
pharmacodynamic assessments such as biomarkers that measure target engagement, HBsAg decline,
HBV DNA decline, HBV RNA decline, and HBcrAg decline to select doses for phase 3 trials.
7. 	Efficacy Endpoints
New finite duraƟon therapies could be evaluated in clinical trials using any of the following efficacy
endpoints:
• 	Sustained suppression (6 months or longer) of HBV DNA (less than LLOQ, TD, or TND) off-
treatment aŌer a finite duraƟon of therapy
• 	Sustained suppression (6 months or longer) of HBV DNA (less than LLOQ, TD, or TND) off-
treatment with HBsAg loss (less than 0.05 internaƟonal unit/milliliter (IU/mL)) with or without
HBsAb seroconversion aŌer a finite duraƟon of therapy
At present, uƟlity of reducƟon in HBsAg from baseline (without complete clearance) for assessing
response to CHB therapies is unclear because of inconsistent correlaƟons between qHBsAg and clinical
response (Hu et al. 2018; Thompson et al. 2010; Chan et al. 2011).
22 See secƟon 505B(a)(2)A) of the FD&C Act.

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A limited number of secondary endpoints (e.g., HBeAg loss, anƟ-HBe seroconversion in HBeAg posiƟve
paƟents, ALT normalizaƟon) should be considered for tesƟng using appropriate staƟsƟcal methods for
mulƟplicity. Biochemical serum markers such as ALT values vary between laboratories, and lack of
normalizaƟon of ALT may oŌen be confounded by the presence of other chronic liver diseases such as
nonalcoholic faƩy liver disease.
Other important endpoints: Assessing progression of liver disease
Except for paƟents with advanced or decompensated cirrhosis, a staƟsƟcally rigorous evaluaƟon of
endpoints of liver progression can be challenging because these events occur infrequently unƟl late in
the course of CHB. However, treatment effects on these endpoints provide useful clinical informaƟon,
and trials evaluaƟng them could be used to support an expanded indicaƟon or paƟent populaƟon and
could be summarized in appropriate secƟons of the label.
Some of the parameters or clinical outcomes that sponsors can consider include the following:
• 	Change in Model for End Stage Liver Disease scores
• 	Change in Child-TurcoƩe-Pugh scores
• 	Progression to liver failure requiring transplantaƟon or resulƟng in death
• 	Occurrence of HCC
Treatment-related regression of fibrosis or cirrhosis, as assessed by liver biopsy or noninvasive methods,
may be appropriate for display in the label. However, sponsors should discuss with the Division plans for
labeling and performance characterisƟcs of the noninvasive modality when protocols evaluaƟng these
endpoints are being designed.

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21
PaƟent-Reported Outcome Measures
Sponsors who are considering incorporaƟng paƟent-reported outcome measures23 as endpoints in
clinical trials to measure treatment benefit should discuss paƟent-reported outcome instruments with
the Agency during the clinical development process.
8. 	Trial Procedures and Timing of Assessments
Biochemical, serological, virological, and histological endpoints can be used to assess the effecƟveness of
therapy. For drugs with finite treatment duraƟons, the opƟmal Ɵme point to assess the primary efficacy
endpoint of sustained virologic response is 6 months or longer aŌer cessaƟon of therapy. AddiƟonally,
the most appropriate Ɵme point to assess efficacy endpoints depends on the mechanism of acƟon and
half-life of the drug. Longer term follow-up may be useful to confirm durability of treatment response
and to measure clinical outcomes.
9. 	StaƟsƟcal ConsideraƟons
In general, a detailed protocol and SAP staƟng the trial hypotheses, analysis methods, and all other
relevant details should be provided to the Division of AnƟvirals before trial iniƟaƟon. To improve the
precision of treatment effect esƟmaƟon and inference, sponsors should consider adjusƟng for
prespecified baseline factors that are anƟcipated to be prognosƟc of the outcome (e.g., HBeAg status,
HBV DNA level, and HBsAg level). If randomizaƟon is straƟfied by baseline covariates, the analysis should
account for the straƟficaƟon factors. A discussion of how the analyses will account for the straƟfied
randomizaƟon should be included in the protocol. For details see the draŌ guidance for industry
AdjusƟng for Covariates in Randomized Clinical Trials for Drugs and Biological Products (May 2021).24 For
staƟsƟcal analysis methods and issues, see the guidances for industry Providing Clinical Evidence of
EffecƟveness for Human Drug and Biological Products (May 1998), Non-Inferiority Clinical Trials to
Establish EffecƟveness (November 2016), and AdapƟve Designs for Clinical Trials of Drugs and Biologics
and the FDA white paper StaƟsƟcal ConsideraƟons on Subgroup Analysis in Clinical Trials (Alosh et al.
2015).
23 See the guidance for industry PaƟent-Reported Outcome Measures: Use in Medical Product Development to
Support Labeling Claims (December 2009).
24 When final, this guidance will represent the FDA’s current thinking on this topic.

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22
a. 	Analysis populaƟons
All subjects who are randomized and received at least one dose of assigned therapy during the trial
should be included in the primary efficacy analysis for all fully blinded trials. For unblinded/parƟally
blinded trials, all randomized subjects should be considered. Any possibility of randomized subjects who
do not receive treatment in either or both arms should be minimized.

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b. 	Efficacy analyses
The primary analysis should compare the proporƟon of responders across trial treatment arms. This
analysis determines whether effecƟveness has been demonstrated.
For subgroup analyses, the analysis of the primary efficacy endpoint should be performed within
important demographic and baseline characterisƟcs (e.g., geographic region, sex, race, age group, HBV
genotype, HBeAg status, screening HBV DNA, baseline weight, body mass index, baseline ALT, baseline
fibrosis/cirrhosis, and (if applicable) prior response to previous treatment regimens). The purpose of
these analyses is to explore the consistency of the primary efficacy endpoint result across these
subgroups.
Treatment-by-region interacƟon should be invesƟgated and reported to assess consistency of the efficacy
results. Treatment-by-HBeAg status interacƟon should also be invesƟgated if HBeAg-posiƟve and HBeAg-
negaƟve subjects are enrolled in the trial.
c. 	Handling missing data
Sponsors should make every aƩempt to limit disconƟnuaƟon of subjects from the trial. When the loss is
unavoidable, sponsors should explain the causes of missing data and aƩempt to determine the final
status of a subject who does not complete the protocol. Analyses excluding subjects with missing data
or other posƩreatment outcomes can be biased because subjects who do not complete the trial may
differ substanƟally in both measured and unmeasured ways compared with subjects who remain in the
trial. The primary method of handling missing data in the analysis should be prespecified in the protocol
and SAP. SensiƟvity analyses should demonstrate that the primary analysis results are robust to the
assumpƟons regarding missing data.
10. 	Accelerated Approval (Subpart H/I) ConsideraƟons
For CHB, HBV DNA suppression with or without HBsAg loss is considered a validated surrogate endpoint
that has been demonstrated to predict clinical outcomes, and this endpoint could be used to support a
tradiƟonal approval. Sponsors should discuss with the FDA plans to use any other surrogate endpoints
that are reasonably likely to predict clinical benefit to support accelerated approval. 25 Accelerated
25 See section 506(c) of the FD&C Act; 21 CFR part 314, subpart H; 21 CFR part 601, subpart E.

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approval is subject to the requirement that postmarkeƟng confirmatory trials are conducted to verify
and describe the anƟcipated effect on irreversible morbidity or mortality or other clinical benefit. 26
11. 	Benefit-Risk ConsideraƟons
A thorough and comprehensive benefit-risk assessment ensures that the benefits outweigh potenƟal
risks to the intended populaƟon. A benefit-risk assessment takes into consideraƟon the demonstrated
therapeuƟc effect of the new drug and observed safety profile in the context of underlying disease and
current treatment opƟons available for the indicaƟon.
C. 	Other ConsideraƟons
1. 	Clinical Virology ConsideraƟons
Samples for HBV quanƟficaƟon, genotypic, and phenotypic analysis should be obtained at different Ɵme
points during treatment and follow-up. Timing of sample collecƟon should be based on iniƟal
observaƟons of potency and on-treatment and off-treatment durability. The genotypes and phenotypes
of baseline and virologic failure isolates should be determined (virologic failure defined as a confirmed
increase of greater than or equal to 1 log 10 HBV DNA copies/mL above nadir, quanƟfiable HBV DNA of
greater than or equal to 1 log10 copies/mL above LLOQ aŌer being less than LLOQ, or never achieved
HBV DNA levels less than LLOQ for two consecuƟve visits). Transient increases in HBV DNA aŌer the
compleƟon of treatment with a finite regimen may occur before sustained suppression. A strategy for
disƟnguishing treatment failures from subjects experiencing a temporary increase should be agreed
upon with the Division during protocol development.
Clinical assessment during the development of acƟvators of the immune system is likely to be
challenging, given that the greatest impact of these types of drugs will likely be a reducƟon in infected
cells resulƟng in depleƟon of the cccDNA reservoir. Complete depleƟon of the cccDNA reservoir to
below the limit of detecƟon may take a long Ɵme and will vary depending on the mechanism of acƟon of
the drug. Currently, the only biomarker sufficient to predict a sustained response off-treatment is HBsAg
loss, the assessment of which may be complicated by HBsAg expressed from integrated HBV DNA
genome fragments. In addiƟon to host immune markers and serum HBV DNA, clinical trial protocols
should assess several exploratory HBV endpoints (HBcrAg, HBV RNA, etc.) early in the development
program in an aƩempt to idenƟfy potenƟal markers that correlate with the drug’s acƟvity and may
predict response to therapy.
26 See 21 CFR 314.510; 21 CFR 601.41.

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Genotypes of baseline and on-therapy virologic failure isolates should be compared and newly emerged
drug resistance-associated subsƟtuƟons/mutaƟons should be idenƟfied. HBV DNA from subjects with
genotypic resistance to the invesƟgaƟonal drug should be cloned in an HBV genome background and
suscepƟbility to the invesƟgaƟonal drug should be determined.
• 	There are 10 recognized HBV genotypes (genotypes A through J) as well as subtypes idenƟfied
for genotypes A through F. The different HBV genotypes/subtypes encode disƟnct viral proteins
and may exhibit differenƟal responses to an invesƟgaƟonal drug, which could confound efficacy
results in clinical trials if the drug is only effecƟve against some genotypes/subtypes (Congly et
al. 2013). Therefore, we recommend determining the genotypes/subtypes of HBV infecƟon
present at baseline to determine if the invesƟgaƟonal drug exhibits anƟviral acƟvity against all
HBV genotypes/subtypes. For subjects with suppressed HBV DNA at baseline, historical
genotype assessments may be used if available. The assay, with performance characterisƟcs,
used to genotype the HBV samples in enrolled subjects should be included with the clinical trial
protocol. It may be important to confirm the genotype/subtype by phylogeneƟc analysis.
• 	For resistance analyses, any changes, including mixtures, in the amino acid sequence of the
target protein or DNA sequence for genome targeƟng drugs, present in on-treatment or follow-
up samples but not in the baseline sample, can be reported as having developed during therapy.
In addiƟon, baseline samples should be analyzed to idenƟfy HBV geneƟc polymorphisms that are
associated with differenƟal anƟviral acƟvity against the invesƟgaƟonal drug. Sponsors should
consult the FDA early for the most current format for submission of resistance data and if Next
GeneraƟon Sequencing (NGS) will be used.
• 	There is a risk of developing resistance against an anƟviral drug that targets similar viral proteins
in different virus species in paƟents coinfected with HIV and HBV. Because of this risk, we
recommend assessing for the development of resistance and cross-resistance in the viral
proteins of both HIV-1 and HBV when appropriate.
• 	For all virologic assessments in clinical trials, we recommend the use of FDA-approved or FDA-
cleared assays, when available, and a central laboratory. Sponsors can collect results from local
lab tests, idenƟfying the assays used. If invesƟgaƟonal assays are used, performance
characterisƟcs of the assays determined from analyƟcal validaƟon studies using geographically
and temporally disƟnct isolates should be provided in addiƟon to detailed descripƟons of the
methodology. 27 Drugs that require assays to idenƟfy the infected populaƟon benefiƟng from
27 See the IDE (Investigational Device Exemption) web page, available at
https://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/HowtoMarketYourDevice/InvestigationalDevi
ceExemptionIDE/ucm046164.htm.

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treatment (e.g., specific genotypes or resistant populaƟons) may require a companion
diagnosƟc. AddiƟonal recommendaƟons can be found in the draŌ guidance for industry and
Food and Drug AdministraƟon staff Principles for Codevelopment of an In Vitro Companion
DiagnosƟc Device with a TherapeuƟc Product (July 2016). 28
• 	Sponsors are encouraged to submit a resistance monitoring plan early in development. If
resistance evaluaƟon in clinical trials involves NGS, we recommend that sponsors discuss details
of the NGS approach with the FDA. Submission of NGS data in FASTQ format is strongly
encouraged. AddiƟonal recommendaƟons can be found in the guidance for industry technical
specificaƟons document Submiƫng Next GeneraƟon Sequencing Data to the Division of AnƟviral
Products (July 2019).
• 	HBV should be genotyped for any instances where HBV DNA is detected in long-term follow-up
to disƟnguish relapse from reinfecƟon.
28 When final, this guidance will represent the FDA’s current thinking on this topic.

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2. 	PharmacokineƟc/Pharmacodynamic ConsideraƟons
Trials conducted in HBV-infected subjects should include assessment of PK and the relaƟonship between
drug exposure (e.g., minimum or maximum plasma concentraƟon (C min or C max ), area under the curve) and
virologic success and toxicity in all subjects.
Sponsors can use a combinaƟon of intensive and sparse sampling throughout development to
characterize the PK of the invesƟgaƟonal drug. For example, sponsors should implement an intensive
sampling schedule in early phase monotherapy trials. In longer term trials, an intensive sampling
schedule might not be feasible. AlternaƟvely, sponsors can combine sparse sampling from these trials
with intensive PK data from earlier trials for populaƟon PK analysis. Sponsors should obtain mulƟple
sparse PK samples from as many subjects as possible, including at the Ɵme of key virologic assessments.
It is important to document dosing Ɵmes and plasma sampling Ɵmes.
Sponsors can use the following two broad approaches to characterize the relaƟonship between drug
exposure and viral kineƟcs or virologic suppression of the invesƟgaƟonal drug, depending on the
development stage and purpose of the analysis. Both approaches allow for exploraƟon of relevant
covariates.
(1) To aid the design of phase 2b or phase 3 trials, with respect to selecƟon of the dosage regimen, a
mechanisƟc approach relaƟng drug concentraƟons and viral kineƟcs should be considered. A
mechanisƟc modeling approach should also account for the development of resistance to the
invesƟgaƟonal drug and the intended paƟent populaƟon. For combinaƟon therapy, the
potenƟal of addiƟve or synergisƟc anƟviral effects can be incorporated in the model to assist
opƟmizaƟon of the dose combinaƟon.
(2) A simplified analysis relaƟng the proporƟon of subjects with virologic suppression or virologic
failure and appropriate exposure variable (e.g., minimum concentraƟon or area under the
plasma drug concentraƟon versus Ɵme curve) can be used to support evidence of acƟvity and to
support dose selecƟon.
Exposure-response safety analyses should consider the mechanisƟc on-target and off-target effects of the
invesƟgaƟonal drug and adverse events that are more frequent in the invesƟgaƟonal drug arm. 	The
appropriate exposure parameter and modeling approach depends on the invesƟgaƟonal drug and toxicity.

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3. 	Labeling ConsideraƟons
Severe acute exacerbaƟons of CHB may occur aŌer disconƟnuaƟon of anƟ-HBV therapy. HepaƟc
funcƟon should be monitored closely with both clinical and laboratory follow-up for at least several
months in subjects who disconƟnue anƟ-HBV therapy. In certain circumstances, resumpƟon of anƟ-HBV
therapy may be warranted. These concerns should be adequately conveyed in drug labeling.
Development of HIV-1 resistance against anƟ-HBV drugs with acƟvity against HIV-1 is a potenƟal risk that
should be conveyed in labeling.

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GLOSSARY OF ACRONYMS
ALT 	alanine aminotransferase
CC 50 	concentraƟon inhibiƟng 50 percent cell growth
cccDNA 	covalently closed circular DNA
CHB 	chronic hepaƟƟs B
EC 50/90 	effecƟve drug concentraƟon inhibiƟng 50 or 90 percent virus replicaƟon
FD&C Act 	Federal Food, Drug, and CosmeƟc Act
HBeAg 	HBV e-anƟgen
HBsAb 	anƟbody specific to HBsAg
HBsAg 	HBV surface anƟgen
HBV 	hepaƟƟs B virus
HBV DNA 	hepaƟƟs B virus DNA
HCC 	hepatocellular carcinoma
HDV 	hepaƟƟs delta virus
HIV 	human immunodeficiency virus
IFN 	interferon
IgM 	immunoglobulin M
IU 	internaƟonal unit
LLOQ 	lower limit of quanƟficaƟon
mL
NRTI
milliliter
HIV nucleoside/nucleoƟde reverse transcriptase inhibitor
NrtI 	HBV nucleoside/nucleoƟde reverse transcriptase inhibitor
NGS 	Next GeneraƟon Sequencing
NI 	noninferiority
PK 	pharmacokineƟc
qHBsAg 	quanƟtaƟve HBsAg
RNA 	ribonucleic acid
rt 	reverse transcriptase
SAP
TD
staƟsƟcal analysis plan
target detected
TND 	target not detected

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