FDA Approves Hovilpri, an Oral Helicase-Primase Inhibitor for Refractory HSV

The FDA has approved pritelivir (Hovilpri, Asahi Kasei Therapeutics) 100mg tablets for immunocompromised adults with mucocutaneous lesions caused by herpes simplex virus (HSV) infection refractory, with or without documented resistance, to acyclovir, valacyclovir, or famciclovir.

Pritelivir, developed by AiCuris Anti-infective Cures AG (now part of Asahi Kasei Therapeutics), is an oral helicase-primase inhibitor with a mechanism of action distinct from nucleoside analogues, the company said. The FDA noted that immunocompromised patients can have more frequent and serious HSV outbreaks that may respond poorly to available treatments because of viral resistance or intolerance.

Approval was supported by Part C of the phase 3 PRIOH-1 trial, a randomized, open-label, comparator-controlled superiority study in 101 immunocompromised adults with mucocutaneous HSV infection refractory to acyclovir, valacyclovir, or famciclovir. Participants received pritelivir (400mg loading dose on day 1, then 100mg once daily) or investigator's choice treatment (intravenous foscarnet, intravenous or topical cidofovir, or topical imiquimod 5%) for up to 28 days, extended up to 42 days if lesions were improving but not healed. For the primary endpoint, all lesions had healed by day 28 in 63% of pritelivir recipients vs 34% of comparator recipients (adjusted treatment difference, 28.4%; 95% CI, 9.6-47.3).

Through day 42, observed response rates were 82% and 42%, respectively, the company reported. Adverse reactions were less frequent with pritelivir (22% vs 54%), as were discontinuations due to adverse reactions (2% vs 20%). Headache was the most common adverse reaction (6% vs 4%). According to the company, certain acid-reducing agents may reduce pritelivir exposure, potentially decreasing efficacy and leading to resistance, and pritelivir, a breast cancer resistance protein (BCRP) inhibitor, may raise plasma concentrations of BCRP substrates.

Pritelivir received priority review for this indication, according to the FDA, and the company said it also received Fast Track and Breakthrough Therapy designations. Asahi Kasei Therapeutics expects the drug to be available in the US before the end of 2026.

Sources: US Food and Drug Administration. FDA approves drug to treat lesions caused by herpes simplex virus. News release. US Food and Drug Administration; October 9, 2026. Accessed October 11, 2026.

Asahi Kasei Therapeutics. Asahi Kasei Therapeutics announces FDA approval of Hovilpri (pritelivir) tablets for mucocutaneous HSV lesions refractory (with or without resistance) to standard antiviral treatment in immunocompromised adults. Press release. Asahi Kasei Therapeutics; October 9, 2026. Accessed October 11, 2026.