Hepcludex, Gilead’s brand of bulevirtide, is one of the more unusual peptide drugs to reach the American market.
It is a synthetic 47-amino-acid lipopeptide designed from a section of the hepatitis B virus’s own surface protein. On May 22, 2026, it became the first FDA-approved treatment for chronic hepatitis delta, widely considered the most severe form of viral hepatitis.
Six months later, Gilead brought new research to the American Association for the Study of Liver Diseases’ Liver Meeting in Denver, held November 5–9.
The presentations examined longer-term responses to bulevirtide, changes in portal hypertension, the interpretation of liver fibrosis tests and a problem that no pharmaceutical breakthrough can solve on its own: many Americans with chronic hepatitis B are not being tested for hepatitis D.
That gap has become harder to ignore now that the United States has an approved medicine specifically intended to treat the infection.
The science behind Hepcludex is clever. Its clinical evidence is increasingly substantial. But the medicine can only reach patients whose infection has first been identified.
How Hepcludex Uses a Viral Peptide to Block Hepatitis D
Hepatitis delta virus, or HDV, has an unusual biological dependency.
It cannot establish an infection without hepatitis B virus, or HBV, because it relies on proteins from hepatitis B to assemble its outer envelope and enter new liver cells.
That relationship explains why hepatitis delta occurs only in people who also have hepatitis B infection.
The two viruses use the same molecular entry point on liver cells: sodium taurocholate co-transporting polypeptide, or NTCP, a transporter normally involved in moving bile acids into hepatocytes.
Hepatitis B uses part of its large surface protein, known as the pre-S1 region, to bind to this receptor.
Bulevirtide is a synthetic peptide derived from that viral region.
According to the US prescribing information, the drug contains 47 amino acids and carries a myristoyl fatty-acid modification at one end of the molecule.
That modification makes it a lipopeptide, a peptide with an attached lipid component.
Rather than attacking the virus directly, bulevirtide binds to NTCP on the surface of liver cells, preventing hepatitis delta virus from attaching to the receptor and initiating infection of those cells.
The strategy is fundamentally different from medicines that inhibit viral replication inside already infected cells.
Bulevirtide acts at the entry stage. It can interfere with the spread of HDV to additional hepatocytes, but it does not directly eliminate every cell that is already infected.
This distinction helps explain why prolonged treatment and the possibility of stopping therapy are major questions in the drug’s clinical development.
Hepcludex uses a piece of the virus’s own entry machinery to block the doorway into liver cells.
The molecule also demonstrates how differently lipid chemistry can be used in peptide medicines.
As Grey Pepper explored in its explanation of semaglutide’s fatty-acid engineering, attaching a lipid can profoundly change how a peptide behaves in the body.
In semaglutide, fatty-acid engineering helps prolong drug exposure through albumin binding. In bulevirtide, the viral-derived peptide and its lipid modification form part of an entry-inhibiting antiviral design.
The underlying chemistry belongs to the same broad field. The therapeutic jobs are very different.
What the Hepcludex Phase 3 Trial Actually Proved
The FDA granted Hepcludex accelerated approval on May 22, 2026, for adults with chronic hepatitis delta infection who do not have cirrhosis or who have compensated cirrhosis.
Compensated cirrhosis means advanced liver scarring is present, but the liver has not yet developed major complications associated with decompensation.
The approval was based primarily on MYR301, a randomized, open-label Phase 3 trial comparing bulevirtide treatment against a delayed-treatment control.
The broader original study included three randomized groups. The principal comparison presented in the US prescribing information involved 101 adults: 50 assigned to immediate treatment and 51 assigned to delayed treatment.
Participants in the immediate-treatment group received daily subcutaneous bulevirtide for 144 weeks.
Those assigned to delayed treatment received no HDV-specific study treatment during the first 48 weeks, after which they could begin bulevirtide.
An important dosing detail is that the MYR301 protocol originally specified 10 mg, but a subsequent dose-recovery study established that the delivered amount was 8.5 mg.
The approved US dose is therefore 8.5 mg by subcutaneous injection once daily.
At week 48, the trial’s combined primary endpoint required two findings: a substantial reduction in HDV RNA, indicating a virologic response, and normalization of alanine aminotransferase, or ALT, a liver enzyme associated with liver injury.
A virologic response could mean HDV RNA became undetectable or declined by at least 2 log10 units from baseline, representing a reduction of at least 99%.
Forty-eight percent of participants receiving bulevirtide achieved the combined response at week 48, compared with 2% in the delayed-treatment group.
The FDA reported a 46-percentage-point difference between the groups, with a 96% confidence interval of 31 to 61 percentage points.
When the components were examined separately, 76% of immediately treated participants achieved the defined virologic response compared with 4% in the delayed group.
ALT normalization occurred in 56% of bulevirtide-treated participants versus 12% of delayed-treatment participants.
Those were meaningful differences in markers of disease activity.
But the distinction between reduced viral load and completely undetectable virus is important.
At week 48, 20% of the bulevirtide group had undetectable HDV RNA. That proportion rose to 36% at week 96 and 50% at week 144 among patients in the immediate-treatment arm.
The longer-term figures describe outcomes observed during ongoing treatment. They are not evidence that half of patients were cured after stopping the drug.
Similarly, the later percentages cannot be compared with the delayed-treatment group’s original 48-week control period as though both groups remained untreated or received identical exposure throughout follow-up.
At 48 weeks, 48% met the combined response endpoint on treatment versus 2% with delayed treatment. That supports antiviral activity, not yet a proven reduction in liver failure or death.
Why Accelerated Approval Does Not Mean the Evidence Is Finished
Hepcludex received accelerated approval rather than traditional approval based on established improvements in long-term clinical outcomes.
The FDA accepted reductions in HDV RNA and normalization of liver enzymes as surrogate measures reasonably likely to predict clinical benefit.
The agency explicitly states that improvement in disease-related clinical outcomes has not yet been established.
That includes questions about whether treatment reduces liver failure, hepatocellular carcinoma, liver transplantation or death.
These are especially important outcomes because hepatitis delta can accelerate the progression of liver disease in people who also have hepatitis B.
Continued US approval may depend on confirmatory studies verifying and describing clinical benefit.
There are also significant treatment-management considerations.
The US label carries a boxed warning about severe acute exacerbations of hepatitis D and hepatitis B after discontinuing Hepcludex.
Patients with cirrhosis may face greater risks of severe flares or progression to hepatic decompensation.
The prescribing information recommends close clinical and laboratory monitoring for at least six months following discontinuation, including HBV DNA and HDV RNA testing.
Common adverse reactions reported in the Phase 3 safety analysis included injection-site reactions, headache, abdominal pain, fatigue and itching.
Hypersensitivity reactions, including anaphylaxis, are also identified in the prescribing information.
The medicine therefore represents an important new option, but it is not a simple one-time intervention that eliminates the need for specialist follow-up.
Its clinical success depends on selecting appropriate patients, maintaining therapy, monitoring treatment response and managing the risks associated with stopping.
What Gilead Presented at The Liver Meeting 2026
Gilead’s October 22 announcement identified eight accepted abstracts involving hepatitis delta for The Liver Meeting 2026 in Denver.
They addressed several questions that become more important once a new antiviral moves from clinical development into routine treatment.
One presentation, abstract 3203, examined the combined virologic and biochemical response with bulevirtide 10 mg monotherapy through 96 weeks.
Another, abstract 3243, examined clinically significant portal hypertension after 48 weeks of treatment, drawing on pooled Phase 2 and Phase 3 data.
Portal hypertension refers to elevated blood pressure in the circulation that carries blood into the liver. It can develop as liver disease progresses and is associated with serious complications of cirrhosis.
That makes the subject clinically important, although the abstract title alone cannot establish how much improvement occurred or which patients benefited.
Other presentations explored ALT flares during treatment with bulevirtide and pegylated interferon, changes in noninvasive measures of liver fibrosis and the value of HDV RNA measurements after therapy.
The last question is particularly important for a drug administered every day.
If HDV RNA becomes undetectable during therapy, clinicians still need to understand whether the response is durable after discontinuation and which patients can safely attempt treatment cessation.
Gilead’s conference announcement provided the titles and areas of investigation, but not the full numerical results for each analysis.
Consequently, the meeting program should not be interpreted as demonstrating new reductions in portal hypertension, improvements in survival or a validated strategy for stopping therapy without examining the underlying poster datasets.
The studies show where the company’s research is moving: toward longer treatment periods, clinically meaningful disease outcomes and management decisions that extend beyond viral-load reduction.
That agenda sits alongside growing interest in other forms of liver treatment, including the metabolic therapies discussed in Grey Pepper’s coverage of Wegovy and Rezdiffra at the 2026 Liver Meeting.
The diseases and medicines are different, but they share a central development challenge: favorable changes in biomarkers must eventually translate into better outcomes for patients.
The Hepatitis D Testing Gap May Be the Bigger Problem
The most revealing part of Gilead’s Liver Meeting program may not have involved a new treatment result.
Abstract 4080, presented on November 8, was titled “Hepatitis Delta Testing Rates Remain Low Among Individuals with Chronic Hepatitis B: A US Administrative Claims Analysis.”
A second claims-based study, abstract 3216, examined disease progression among commercially insured patients with hepatitis delta in the United States.
Gilead’s announcement described the testing analysis as evidence of a persistent care gap, but it did not provide the numerical testing rate in the public release.
Earlier published US research gives that concern more concrete context.
A multicenter study examining 13,218 patients with chronic hepatitis B across three US safety-net health systems reported that only 6.1% had received anti-HDV antibody testing.
Among those tested, 15.7% had positive HDV antibody results.
The study also identified a substantial gap between antibody positivity and subsequent RNA testing to determine whether active viral infection was present.
These figures come from a specific safety-net patient population and an earlier study period. They should not be treated as the national testing rate in November 2026.
Nevertheless, they illustrate why a person can live with hepatitis B for years without receiving the additional testing needed to identify hepatitis delta.
That has consequences because HDV can cause more aggressive liver disease than hepatitis B infection alone.
The availability of Hepcludex changes the practical importance of diagnosis.
Before US approval, identifying chronic hepatitis delta could help clinicians characterize risk, monitor progression and consider available or investigational treatment options.
Now, identifying active HDV infection can also lead to consideration of an FDA-approved, HDV-specific antiviral treatment for eligible adults.
A first-in-class medicine cannot treat an infection that the healthcare system has never looked for.
A New AASLD Recommendation Makes the Testing Question Harder to Ignore
The testing debate also received an important update immediately before the November Liver Meeting presentations.
In November 2026, the American Association for the Study of Liver Diseases published an expert practice opinion on hepatitis delta diagnosis and management.
Its central screening recommendation is straightforward: everyone who tests positive for hepatitis B surface antigen, or HBsAg, should receive HDV antibody testing at least once.
Those with positive HDV antibody results should then undergo HDV RNA testing to confirm active infection.
These are different tests with different purposes.
HBsAg testing identifies hepatitis B infection. Anti-HDV testing identifies evidence of exposure to hepatitis delta. HDV RNA testing determines whether the virus is currently detectable in the bloodstream.
A positive antibody test alone does not establish that someone has ongoing HDV replication or automatically qualifies them for antiviral therapy.
The World Health Organization’s 2024 hepatitis B guidelines had already supported broad HDV antibody testing among people who are HBsAg-positive, with laboratory reflex testing as a strategy to improve access.
Reflex testing means that a laboratory can automatically perform an additional test after a qualifying result, where the necessary specimen and testing arrangements are available.
That approach can reduce the number of separate appointments and specimen collections needed to complete the diagnostic process.
The new AASLD opinion reinforces the need to move beyond narrowly targeted screening toward more consistent identification of HDV among people with hepatitis B.
It also recommends further liver assessment and regular monitoring for people diagnosed with chronic hepatitis delta.
For eligible adults with chronic HDV viremia and compensated liver disease, bulevirtide can now be considered as an HDV-specific treatment option.
But that clinical pathway only works when each step occurs: hepatitis B identification, hepatitis delta screening, confirmation of active HDV infection, disease assessment and appropriate treatment evaluation.
The bottleneck is no longer simply the absence of an approved medicine. It is also the ability to identify people who might benefit from one.
Why the Drug’s European History Matters
Although Hepcludex is new to the American market, bulevirtide is not new to clinical use internationally.
The European Medicines Agency granted Hepcludex conditional marketing authorization in July 2020.
That authorization was converted into standard marketing authorization in July 2023, providing European clinicians with several years of treatment experience before the US approval.
The European regimen has commonly used a 2 mg daily dose, while the approved US regimen uses 8.5 mg daily.
These differences should not be interpreted as evidence that one dose is necessarily more effective or safer than the other without examining the relevant clinical studies.
They do, however, mean that international safety experience and long-term treatment observations can contribute to the broader understanding of bulevirtide.
Experience outside the United States may also help researchers investigate which patients respond, how clinicians monitor therapy and what happens after treatment is discontinued.
That last question remains particularly important because treatment-associated viral suppression does not automatically establish sustained control after the medicine is stopped.
What Still Needs to Be Proven About Hepcludex
The strongest available evidence supports bulevirtide’s ability to improve virologic and biochemical markers in chronic hepatitis delta.
But several questions remain unresolved.
The first is whether sustained treatment reduces major clinical complications such as hepatic decompensation, liver transplantation, liver cancer and liver-related mortality.
Those outcomes matter more to patients than viral-load measurements alone, although viral suppression can be an important step toward achieving them.
The second is treatment duration.
A daily injection may be manageable for some patients, but long-term treatment requires continuing access, adherence and monitoring.
Researchers need to identify whether any patients can stop therapy safely, how durable their responses remain and which factors predict relapse or severe hepatitis flares.
The third is whether improvements in noninvasive liver fibrosis measurements accurately reflect structural improvements in the liver.
Changes in liver stiffness can be useful, but inflammation and other factors can affect those measurements. A favorable result is not automatically proof that liver scarring has reversed.
The fourth is access.
FDA approval establishes a regulatory pathway for treatment, but it does not guarantee that every eligible patient will receive the medicine.
Patients may still face diagnostic delays, specialist referral barriers, insurance restrictions, treatment costs or practical difficulties associated with daily injections.
Those challenges may be especially consequential when a disease has historically been underdiagnosed.
Finally, the true size of the undiagnosed hepatitis delta population in the United States remains uncertain.
Estimates depend heavily on the populations studied, the frequency of antibody screening and the availability of confirmatory RNA testing.
Improving testing will therefore do more than help find patients. It will also improve researchers’ understanding of how common the disease actually is.
What Comes Next for Hepatitis D Treatment in America
The next phase of Hepcludex’s US story will unfold across two different systems.
In clinical research, investigators will continue studying longer treatment durations, the durability of HDV suppression, markers of liver disease progression and clinical outcomes that can verify the drug’s benefit beyond surrogate endpoints.
In healthcare delivery, hepatologists, primary-care clinicians and laboratories will need to translate hepatitis delta screening recommendations into routine practice.
That may involve more consistent one-time anti-HDV testing for people with chronic hepatitis B, greater availability of reflex testing and clearer pathways from a positive result to specialist evaluation.
The new AASLD expert opinion makes the desired direction clear. The November conference research shows why implementation remains important.
Hepcludex has already demonstrated that a synthetic peptide modeled on a viral protein can be developed into a clinically active antiviral medicine.
That is a scientific achievement in its own right.
But the most consequential question now extends beyond the molecule: how many people with chronic hepatitis B have an undetected second infection that puts their liver at greater risk?
For decades, American patients with hepatitis delta had no FDA-approved treatment specifically for the disease.
Now there is one.
Hepcludex solved one part of the problem: the absence of an approved antiviral. The harder public-health task is making sure people with hepatitis D are diagnosed early enough to be considered for treatment.
Sources and Further Reading
- US Food and Drug Administration — FDA Approves First Treatment for Chronic Hepatitis Delta Virus Infection. May 22, 2026.
- DailyMed — Hepcludex (bulevirtide-gmod), US Prescribing Information. Revised May 2026.
- Gilead Sciences — Gilead to Present New Data on Treatment Response and Long-Term Management of Rare Liver Diseases at The Liver Meeting 2026. October 22, 2026.
- American Association for the Study of Liver Diseases — New Expert Practice Opinion on Diagnosis and Management of Hepatitis Delta Virus Infection. November 2026.
- Wong RJ, et al. Hepatitis Delta Virus Testing and Prevalence Among Chronic Hepatitis B Patients Across Three US Safety-Net Health Systems. Clinical Gastroenterology and Hepatology, 2025.
- World Health Organization — Guidelines for the Prevention, Diagnosis, Care and Treatment for People With Chronic Hepatitis B Infection. March 2024.
- European Medicines Agency — Hepcludex: Authorization and Product Information.
