Asahi Kasei wins FDA approval for HOVILPRI in refractory HSV
The oral drug's label covers immunocompromised adults whose lesions failed standard antivirals, with U.S. availability expected before the end of 2026.
Adrian Kessler
An oral treatment for refractory herpes simplex lesions won U.S. approval on Friday as Asahi Kasei Corporation OTCMKTSAHKSY said the FDA approved HOVILPRI (pritelivir) for immunocompromised adults. In its pivotal trial, 63 per cent of patients given the drug had complete lesion healing by Day 28, against 34 per cent on investigator's choice.
The Oct. 9 announcement limits the indication to mucocutaneous HSV lesions that remain refractory to acyclovir, valacyclovir or famciclovir, whether or not resistance has been documented. Asahi expects U.S. availability before the end of 2026. That announcement gives no HOVILPRI sales forecast.
Asahi Kasei is a Tokyo-based group whose specialty pharmaceutical business has its U.S. and European headquarters in North Carolina.
The company's U.S. depositary receipts OTCMKTSAHKSY closed at US$20.06 at 4 p.m. EDT on Oct. 9, down 1.57 per cent from the prior close.
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Trial Showed More Complete Healing
Part C of the PRIOH-1 Phase 3 trial randomized and treated 101 immunocompromised adults, Asahi said on Oct. 9. It compared oral pritelivir with an investigator's choice of intravenous foscarnet, intravenous or topical cidofovir, or topical imiquimod. Patients received treatment for up to 28 days, with an extension possible if their lesions were improving.
The trial met its primary endpoint of complete lesion healing through Day 28. Asahi reported an adjusted treatment difference of 28.4 percentage points, with a p value of 0.0047. The 95 per cent confidence interval ran from 9.6 to 47.3 percentage points. The release also reported higher observed healing by Day 42, but the Day 28 result is the comparison supporting the approval.
Adverse reactions occurred in 22 per cent of pritelivir patients and 54 per cent of those on investigator's choice, the company said on Oct. 9. Headache was the most common reaction with HOVILPRI. The prescribing information summarized by Asahi also warns that some acid-reducing drugs can lower pritelivir exposure, potentially weakening treatment or encouraging resistance.
"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," Stacy Wheeler, chief executive of Asahi Kasei Therapeutics in the U.S. and Europe, said in the release.
The Label Defines a Smaller Market
Transplant recipients, people living with HIV and patients with malignancies are among the immunocompromised groups described in Asahi's announcement. The approval does not extend to routine cold sores or recurrent genital herpes in otherwise healthy adults. Neither the Oct. 9 release nor the product page checked Oct. 10 gives a U.S. eligible patient count or a launch price, so those documents do not support a sales estimate based on all HSV infections.
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One listed HSV developer is Assembly Biosciences, Inc. NASDAQASMB. Its pipeline page describes helicase-primase inhibitors for recurrent genital herpes and says its HSV program was exclusively licensed in December 2025. Both approaches target the viral helicase-primase complex, but Assembly's candidates address a different patient group from HOVILPRI's refractory-lesion label.
The iShares Biotechnology ETF NASDAQIBB traded at US$202.70 at 9:33 a.m. EDT on Oct. 9, before Asahi's evening announcement.
Asahi expects HOVILPRI to be available in the United States before the end of 2026, the next milestone for turning the approval into a treatment physicians can prescribe.
