FDA approves Asahi Kasei drug for persistent herpes infections

On October 9, 2026, the FDA approved Asahi Kasei's oral drug pritelivir (Hovilpri) for immunocompromised patients with persistent, treatment-resistant herpes simplex virus lesions. Pritelivir inhibits viral helicase-primase to bypass mutations that cause resistance to older therapies. In the 101-patient PRIOH-1 trial, 62.7% of pritelivir-treated patients achieved complete lesion healing by 28 days compared to 34% on existing treatments. Asahi Kasei expects the drug to serve 15,000 U.S. patients and reach peak sales over $400 million.

FDA approval and target population

• ▪Pritelivir is an oral treatment indicated for patients with weakened immune systems, including those with hematologic malignancies, stem-cell or solid-organ transplants, HIV, or autoimmune diseases
• ▪The U.S. FDA approved pritelivir (Hovilpri) tablets on October 9, 2026, to treat mucocutaneous herpes simplex virus (HSV) lesions in immunocompromised patients who have not responded to existing treatments

PRIOH-1 clinical trial details

• ▪In the phase III PRIOH-1 trial of 101 immunocompromised patients with acyclovir-refractory HSV lesions, 62.7% of patients receiving 100-mg once-daily pritelivir achieved complete lesion healing by 28 days compared to 34% receiving alternative treatments
• ▪The open-label PRIOH-1 trial compared pritelivir against investigator-choice treatments, which included intravenous foscarnet as well as off-label cidofovir and imiquimod

Mechanism of action and resistance

• ▪Pritelivir is an oral helicase-primase inhibitor that blocks proteins the herpes virus needs to copy its genetic material, stopping viral multiplication in strains resistant to nucleoside analogue and foscarnet treatments
• ▪Older first-line antiviral treatments for herpes simplex virus, such as acyclovir, valacyclovir, and famciclovir, require activation by a viral enzyme before blocking replication, allowing viral mutations to disrupt activation and cause resistance

Market size and sales projections

• ▪Asahi Kasei estimated that pritelivir could serve approximately 15,000 immunocompromised U.S. patients
• ▪Asahi Kasei projected that pritelivir could generate peak annual sales exceeding $400 million in the mid-to-late 2030s

FDA priority review

• ▪Prior to its approval, pritelivir was granted priority review status by the U.S. Food and Drug Administration
• ▪Cynthia Wat, MD, chief medical officer for drugmaker Aicuris, stated during pritelivir's priority review that achieving rapid lesion healing while maintaining tolerability is essential for treatment-refractory HSV patients