Bulevirtide, marketed by Gilead as Hepcludex (bulevirtide-gmod), is a 47-amino-acid lipopeptide that blocks the sodium taurocholate co-transporting polypeptide (NTCP), the entry receptor that both hepatitis B and hepatitis D viruses use to infect hepatocytes. By occupying NTCP, the drug stops new viral entry without acting on viral replication directly, an unusual mechanism for an antiviral.
The drug won FDA accelerated approval on May 22, 2026 as the first and only US treatment for chronic hepatitis delta virus (HDV), the smaller satellite virus that requires HBV co-infection and that drives the most aggressive form of viral hepatitis. The approval rested on virologic response and ALT normalization data from European post-marketing experience; bulevirtide had been authorized in the EU since 2020. Because HDV cannot replicate without HBV's surface antigen, an NTCP entry inhibitor lands at the heart of the HBV/HDV functional-cure conversation now playing out across gene editing, epigenetic silencing, and therapeutic vaccines.
Stories here cover bulevirtide's regulatory milestones and the HDV cure race around it. See #hdv, #hbv, and #entry-inhibitor for adjacent threads.
Assembly Biosciences presented topline Phase 1a data on ABI-6250 at EASL 2026 (poster WED-579, Dr. Edward Gane, University of Auckland) — a first-in-class oral hepatitis D virus (HDV) entry inhibitor. The Phase 1a study evaluated safety, pharmacokinetics, and pharmacodynamic activity in healthy participants; the data supports advancing directly into a Phase 2 study by year-end. ABI-6250 is the only oral entry inhibitor in development for chronic HDV. The mechanistic context matters: Gilead's Hepcludex (bulevirtide) — a 47-amino-acid injectable lipopeptide NTCP entry inhibitor — just won FDA accelerated approval May 22 as the first US HDV treatment. ABI-6250 targets the same entry-inhibition step but as an oral small molecule rather than an injectable peptide, positioning it as a potential next-generation convenience competitor in the small but newly-validated HDV market. Assembly also announced May 22 an expansion of ABI-6250 development into cholestatic liver diseases. The peptide-vs-small-molecule dynamic in HDV mirrors the same competition that played out in GLP-1 (injectable semaglutide vs oral orforglipron).
The FDA granted accelerated approval on May 22, 2026 to Gilead Sciences' Hepcludex (bulevirtide-gmod) 8.5 mg, the first and only approved US treatment for adults living with chronic hepatitis delta virus (HDV) infection. Bulevirtide — formerly known as Myrcludex B — is a 47-amino acid, N-terminally myristoylated lipopeptide derived from the pre-S1 domain of the HBV large envelope protein. The molecule binds to the sodium taurocholate cotransporting polypeptide (NTCP) — the entry receptor that HDV and HBV both use to enter hepatocytes — and blocks viral entry as a first-in-class entry inhibitor. The Phase 3 MYR301 trial documented a statistically significant combined virologic and biochemical response at week 48 versus delayed-treatment control, supporting the accelerated-approval threshold. Continued approval depends on confirmatory trial verification of clinical benefit. Bulevirtide has been EU-approved under conditional marketing authorization since 2020. Gilead shares closed Friday at $134.36, up roughly 3%.
Bulevirtide's mechanism reveals why an entry inhibitor succeeded where small-molecule antivirals didn't. HDV is an obligate parasite of HBV — the delta virus uses the HBV envelope to assemble its virions and the HBV-derived large surface protein to enter hepatocytes via the sodium taurocholate cotransporting polypeptide (NTCP) receptor on hepatocyte cell membranes. Existing HBV antiviral nucleoside/nucleotide analogs (entecavir, tenofovir) suppress HBV replication but don't clear circulating HBsAg or interrupt the HDV entry cycle. Bulevirtide's 47-amino acid sequence — derived from the HBV pre-S1 domain — binds NTCP competitively and blocks both HDV and HBV entry. Real-world EU experience since 2020 shows roughly 50-60% of HDV patients achieve undetectable HDV RNA after 96 weeks of treatment, with a favorable safety profile dominated by injection-site reactions. The US approval expands access for an estimated 75,000-100,000 US patients with chronic HDV, most of whom were previously treated empirically with off-label interferon alfa with poor tolerability.