The U.S. Food and Drug Administration on October 9 approved HOVILPRI (pritelivir) 100 mg tablets from Asahi Kasei Therapeutics for mucocutaneous lesions caused by herpes simplex virus (HSV) infections that are refractory — with or without documented resistance — to standard antivirals like acyclovir, valacyclovir, and famciclovir in immunocompromised adults. It is the first new-mechanism FDA-approved therapy for refractory mucocutaneous HSV in nearly 30 years.
Approval was based on the pivotal Phase 3 trial PRIOH-1 Part C, a randomized, open-label, comparator-controlled study of 101 immunocompromised adults with treatment-refractory HSV. The control arm received the investigator's choice of intravenous foscarnet — the main approved alternative — or off-label cidofovir or imiquimod.
By Day 28, 62.7% of HOVILPRI-treated participants achieved complete lesion healing (the company release rounds it to 63%), versus 34% on the control, an adjusted treatment difference of 28.4% (95% CI: 9.6–47.3; p=0.0047). Common side effects included headache, diarrhea, nausea, decreased appetite, vomiting, and dizziness.
HOVILPRI is a first-in-class helicase-primase inhibitor. As Reuters explains, its edge is mechanistic: older first-line drugs must first be activated by a viral enzyme before they can block replication, and mutations that disrupt that activation cause resistance. Pritelivir blocks the proteins the virus needs to copy its genetic material, stopping it from multiplying — and it works against infections resistant to older treatments.
There's a practical benefit too: it's an oral drug, so eligible patients no longer need intravenous infusions — previously the main option for this population.
Pritelivir was developed by German drugmaker AiCuris, which Asahi Kasei acquired in April. "Today's approval delivers the first FDA-approved treatment for refractory mucocutaneous HSV lesions with a novel mechanism of action in nearly 30 years and marks an important advancement for immunocompromised adults," said Stacy Wheeler, CEO of Asahi Kasei Therapeutics in the U.S. and Europe. "HOVILPRI offers a new oral treatment option for adult patients with a persistent, difficult-to-treat disease." The company expects a U.S. launch before the end of 2026.
The review sailed through three FDA expedited programs: Fast Track, Breakthrough Therapy designation, and Priority Review. Asahi Kasei has estimated about 15,000 eligible U.S. patients and peak annual sales above $400 million in the mid-to-late 2030s. On approval day, Asahi Kasei shares closed up 2.62% at $10.30.