FDA approves pritelivir for refractory herpes lesions in immunocompromised adults

The U.S. Food and Drug Administration approved Hovilpri, or pritelivir, on October 9 for immunocompromised adults with herpes simplex virus lesions that have not responded to acyclovir, valacyclovir or famciclovir. The decision adds an oral treatment option for patients whose weakened immune systems can make these infections especially difficult to control.

The approval covers mucocutaneous lesions—those affecting skin or mucosal surfaces. In the supporting randomized trial, complete healing by day 28 occurred in 63% of pritelivir recipients, compared with 34% receiving an investigator-selected alternative. That is a clinically relevant endpoint for persistent lesions, although it does not establish elimination of the underlying infection.

A different antiviral target

Pritelivir is a small-molecule inhibitor of the viral helicase-primase complex, machinery involved in copying viral DNA. Its mechanism provides another approach when commonly used antiviral medicines have failed.

Asahi Kasei Therapeutics, which announced the approval on October 9, said the indication includes refractory infections with or without documented drug resistance. The distinction matters: an infection can fail to improve clinically without laboratory confirmation that the virus carries resistance to a particular medicine.

The company expects U.S. availability before the end of 2026. That remains a prospective commercial timetable; the approval announcement does not establish that patients can already obtain the medicine.

What the trial measured

The registrational Part C of the Phase 3 PRIOH-1 study was randomized, open-label and comparator-controlled. Its treated population comprised 101 adults with compromised immunity. Their underlying conditions included cancers, transplantation, HIV infection and autoimmune or inflammatory diseases.

Participants received pritelivir or an investigator's choice of available treatment. Those alternatives included intravenous foscarnet, intravenous or topical cidofovir, and topical imiquimod. The comparison therefore reflects a group of treatment options rather than a single uniform competing drug.

An investigator presentation reports that 51 participants received pritelivir and 50 received comparator treatment. The adjusted difference in complete healing through day 28 was 28.4 percentage points, with a 95% confidence interval of 9.6 to 47.3 percentage points. The interval supports a treatment advantage while showing uncertainty about its exact size.

The same presentation reported fewer discontinuations attributed to drug-related adverse events with pritelivir: 2%, compared with 20% in the comparator group. These results were available before the approval. The October development is the regulatory decision, rather than the first disclosure of the trial findings.

Safety and limits

FDA identified headache as the most common adverse reaction and highlighted drug-interaction information. The manufacturer's approval materials also warn that certain acid-reducing medicines can lower pritelivir exposure, potentially reducing its effect and contributing to resistance.

Several features constrain interpretation. The trial was relatively small and unblinded, so participants and investigators knew which treatment was given. Different underlying illnesses and different comparator medicines complicate attempts to predict the benefit for an individual patient group. A short-term healing endpoint also cannot establish durable prevention of future outbreaks or longer survival.

The practical advance is an additional treatment for a narrowly defined population facing persistent HSV disease. Its relevance to healthspan lies in managing illness in medically vulnerable adults; the study did not test an aging intervention. Broader claims about routine herpes treatment, transmission prevention or long-term protection would require evidence beyond this approval.