FDA Approves First Treatment for Chronic Hepatitis Delta Virus (HDV) Infection

FDA Approves Hepcludex as First Treatment for Chronic HDV

The U.S. Food and Drug Administration (FDA) has approved Hepcludex (bulevirtide-gmod) injection, developed by Gilead Sciences, Inc., as the first treatment for chronic hepatitis delta virus (HDV) infection in adults without cirrhosis or with compensated cirrhosis. This approval, granted on May 22, 2026, addresses a critical unmet need for patients with this serious, life-threatening condition. Efficacy was demonstrated in the Phase 3 Trial MYR301, where Hepcludex achieved a combined response rate of 48% at week 48, significantly higher than the 2% observed in the delayed treatment group. The drug also received Breakthrough Therapy and Orphan-Drug Designations and was approved via the Accelerated Approval pathway.

• The efficacy of Hepcludex was established in Trial MYR301, a multi-center, randomized, open-label, parallel-arm phase 3 study. Participants were assigned to immediate treatment with Hepcludex 8.5 mg once daily for 144 weeks or delayed treatment with an observational period followed by 96 weeks of Hepcludex. The trial focused on adults with chronic HDV infection, specifically those without cirrhosis or with compensated cirrhosis.
• Beyond the primary combined response, Hepcludex demonstrated increasing rates of undetectable HDV RNA over time. At week 48, 20% of the Hepcludex group achieved undetectable HDV RNA, compared to 0% in the delayed group. This rate further improved to 36% at week 96 and 50% at week 144 in the Hepcludex group, highlighting sustained viral suppression.
• The FDA recognized the significant need for this therapy by granting Hepcludex Breakthrough Therapy Designation and Orphan-Drug Designation. The drug also underwent priority review and was approved under the Accelerated Approval pathway, underscoring the FDA's commitment to expediting access to innovative treatments for diseases with limited or no existing options.
• Possible side effects associated with Hepcludex include hypersensitivity reactions, injection site reactions, headache, abdominal pain, fatigue, and pruritus. Importantly, the labeling includes a boxed warning advising that discontinuation of Hepcludex may lead to severe acute exacerbations of both HDV and HBV infection, requiring careful patient management.

Addressing the Critical Unmet Need in Chronic HDV

Current treatment approaches for chronic HDV infection face significant challenges across multiple domains, from limited therapeutic options to substantial access barriers. Despite recent therapeutic advances, HDV remains the most challenging type of chronic viral hepatitis with response rates still less favorable compared to HBV and HCV.

• Limited efficacy of standard therapy: Pegylated interferon-alpha remains the primary treatment option with unsatisfactory response rates of only 20-40%, high treatment failure rates (44% at week 48), and significant side effects leading to treatment discontinuation

• Restricted access to novel therapies: While bulevirtide has revolutionized the field as an approved entry inhibitor, optimal treatment duration remains undetermined, and it is the only novel anti-HDV agent evaluated in HIV/HBV/HDV coinfection requiring extended treatment durations

• Diagnostic and healthcare system barriers: Major access limitations include high diagnostic costs (identified by 75% of clinicians), limited test availability (41.7%), lack of awareness (66.7%), and absence of national screening guidelines, with HDV diagnostics being unaffordable for most patients despite availability

• Patient tolerance and eligibility issues: Many patients are intolerant to or ineligible for interferon treatment, particularly those with advanced cirrhosis or severe immunosuppression, while interferon-based therapy requires careful management in special populations including HIV coinfected patients

• Treatment duration and monitoring challenges: Eradication of HBsAg as the ultimate therapeutic endpoint may require long-term interferon administration, raising tolerance issues, while the need for extended monitoring and combination strategies remains unclear for optimal patient outcomes

Key Efficacy and Design of the Pivotal Hepcludex Trial

The pivotal clinical trials for chronic hepatitis delta virus (HDV) infection have evolved from early interferon-based studies to recent investigations of novel direct-acting agents like bulevirtide. These studies have employed diverse design approaches ranging from controlled randomized trials to real-world cohort studies, with treatment durations extending from 28 days to over two years.

• Austrian Nationwide Cohort Study (2026): Real-world observational study of 61 patients receiving bulevirtide for median 29.0 months, with primary endpoints of virological response, biochemical response, and combined response assessed every 6 months through M24

• Phase 2/3 Trial (2025): Six-arm randomized study of 90 patients comparing bulevirtide monotherapy and combination regimens over 48 weeks, with primary endpoint of undetectable HDV RNA at week 72 and secondary endpoint of >1 log IU/mL decline in hepatitis B surface antigen

• MYR202 Trial (2022): Multicentre, randomized, open-label phase 2 trial of 120 patients comparing three bulevirtide doses (2 mg, 5 mg, 10 mg) plus tenofovir versus tenofovir alone for 24 weeks, with primary endpoint of undetectable HDV RNA or ≥2 log IU/mL decline at week 24

• HIDIT Trials (2020): Two parallel, double-blind randomized controlled trials at 14 sites enrolling 120 patients comparing peginterferon alfa-2a plus tenofovir versus peginterferon alfa-2a plus placebo for 96 weeks, with primary endpoint of undetectable HDV RNA at end of treatment

• REP 301 Trial (2018): Open-label, non-randomized phase 2 trial of 12 patients receiving sequential REP 2139 monotherapy, combination with pegylated interferon alfa-2a, then pegylated interferon alfa-2a monotherapy over 63 weeks total, with primary endpoints of safety and tolerability

• Lonafarnib Phase 2A Trial (2016): Double-blind, randomized, placebo-controlled study of 14 patients comparing lonafarnib 100 mg versus 200 mg twice daily for 28 days, with primary therapeutic endpoint of decrease in HDV RNA viral titre and primary safety endpoint of treatment tolerability

Safety and Tolerability Profile of Hepcludex

Clinical trials for chronic hepatitis delta virus (HDV) infection have revealed distinct safety profiles across different therapeutic approaches. The most recent data from Phase 3 bulevirtide trials and Phase 2 PEG IFN-lambda studies provide comprehensive safety information for emerging treatments, while historical interferon data highlights longstanding tolerability challenges.

• Bulevirtide demonstrates a favorable safety profile with the most common adverse events including headache, pruritus, fatigue, eosinophilia, injection-site reactions, upper abdominal pain, arthralgia, and asthenia being more frequent in treatment groups versus control, though no treatment-related serious adverse events occurred through 96 weeks of treatment

• PEG IFN-lambda-1a shows manageable but notable hepatic safety signals with flu-like symptoms and elevated transaminase levels as common adverse events, while 24% of patients experienced hyperbilirubinemia with or without liver enzyme elevation requiring drug discontinuation, particularly in the Pakistani cohort

• Lonafarnib exhibits dose-dependent gastrointestinal toxicity as its primary safety concern, though tolerability improves when combined with ritonavir due to enhanced hepatic drug concentrations allowing for lower dosing

• Traditional pegylated interferon alfa carries significant safety burdens including psychiatric adverse events (historical cases of suicide), hyperthyroidism, and poor tolerability especially in patients with advanced cirrhosis, limiting its clinical utility despite being the only treatment option for approximately 40 years

• Patient-reported outcomes reveal substantial disease burden with fatigue being the most severe and burdensome symptom impacting daily functioning, emotional wellbeing, physical capacity, social engagement, and work productivity independent of treatment-related adverse events

Hepcludex's Impact on the Evolving HDV Treatment Landscape

The chronic hepatitis delta virus (HDV) treatment landscape has undergone significant transformation over the past five years, marked most notably by the emergence of bulevirtide (BLV) as the first approved therapy for this indication. Bulevirtide, a first-in-class entry inhibitor that blocks the sodium taurocholate co-transporting polypeptide receptor, received conditional approval from the European Medicines Agency in 2020, followed by full European Union approval in July 2023. The pivotal MYR301 phase III study demonstrated sustained efficacy across 96 weeks of treatment, with combined response rates (undetectable HDV RNA or ≥2 log decline plus ALT normalization) maintained between the 2 mg and 10 mg daily doses. Notably, 95% of the 150 enrolled patients completed the 96-week study period, with improvements in liver stiffness observed and predominantly mild adverse events reported.

The development pipeline has expanded substantially with multiple novel therapeutic approaches progressing through clinical trials. Lonafarnib, a prenylation inhibitor that disrupts HDV virion assembly, has advanced to phase III development following promising phase II results in the LOWR-2 study. When combined with ritonavir and pegylated interferon-alpha, lonafarnib achieved primary endpoint response rates of 89% in 24-week treatment regimens, though gastrointestinal toxicity remains dose-limiting. PEG IFN-lambda-1a, which targets interferon-lambda receptors predominantly expressed in hepatocytes, demonstrated intention-to-treat virologic response rates of 36% at the 180 mcg dose in the LIMT-1 trial, with ongoing phase III development. Additionally, nucleic acid polymers (NAPs) like REP 2139-Mg have shown promise in blocking HBsAg production, while investigational agents tobevibart (VIR-3434) and elebsiran (VIR-2218) are advancing through phase II and III trials with demonstrated pan-genotypic activity.

Despite these therapeutic advances, significant treatment gaps persist globally, with no FDA-approved therapies available as of 2022 and substantial diagnostic barriers limiting patient access to care. Real-world data from diverse populations reveal concerning patterns: in New York City, only 5.1% of HBV patients received HDV testing, while in Pakistan, HDV RNA PCR testing remains limited due to cost and availability constraints. The data from Mongolia particularly highlights the disease burden, with 78.6% of patients with advanced chronic liver disease testing positive for anti-HDV, yet only 25% had previously received anti-HBV therapy. These findings underscore that while the treatment landscape has evolved dramatically with new therapeutic options demonstrating excellent antiviral activity, addressing diagnostic gaps and treatment accessibility remains critical for translating these advances into improved patient outcomes.

First FDA Approval Marks Breakthrough in HDV Therapy

The recent FDA approval of Hepcludex (bulevirtide) for chronic hepatitis delta virus (HDV) infection marks a transformative moment for patients grappling with this severe and often rapidly progressive liver disease. For decades, treatment options were severely limited, with pegylated interferon-alpha offering only modest efficacy and significant tolerability challenges, leaving a substantial unmet medical need. Bulevirtide, as a first-in-class entry inhibitor, represents a paradigm shift by directly targeting the NTCP receptor, thereby blocking the virus's ability to infect liver cells.

This approval not only establishes a new standard of care but also positions bulevirtide as a foundational therapy in the HDV landscape. Strategic implications include the potential for combination therapies, as studies indicate synergistic effects when bulevirtide is used with pegylated interferon-alpha, and ongoing research explores its integration with other novel compounds like lonafarnib and nucleic acid polymers. Such combinations could enhance antiviral responses and potentially move closer to achieving HBsAg loss, which is considered the closest to a functional cure.

However, important considerations remain. While efficacy has been demonstrated through 96 weeks, the optimal duration of bulevirtide therapy and its long-term impact on achieving HBsAg clearance require further elucidation. Additionally, an asymptomatic increase in bile acids has been observed, necessitating continued monitoring and understanding of its clinical significance. Despite these points, real-world data are emerging, showing promising results in patients with more advanced disease, including those with decompensated cirrhosis and individuals awaiting liver transplantation. While these observations are encouraging, controlled trials are essential to confirm safety and efficacy in these complex populations, potentially expanding the drug's approved indication in the future. This approval is a significant step forward, but the journey towards a complete cure for HDV continues with ongoing research and development.