Asahi Kasei Therapeutics has received approval from the US Food and Drug Administration (FDA) for HOVILPRI (pritelivir), an oral treatment for difficult-to-treat herpes simplex virus (HSV) infections in adults with weakened immune systems. The medicine is approved for mucocutaneous lesions that do not respond to standard antiviral treatments, including cases with or without documented drug resistance.
The approval marks an important development for patients whose infections persist despite treatment with antiviral medicines such as acyclovir, valacyclovir or famciclovir. HOVILPRI is the first FDA-approved treatment for these difficult-to-treat HSV lesions with a new mechanism of action in nearly 30 years, according to the company.
The FDA decision is based on results from the Phase 3 PRIOH-1 clinical trial, which evaluated pritelivir in immunocompromised adults with HSV infections that were resistant to, or did not respond to, standard antiviral therapy.
In the study, 63% of patients receiving HOVILPRI achieved complete lesion healing by Day 28, compared with 34% of patients receiving investigator-selected alternative treatments. The results showed a statistically significant improvement in healing with HOVILPRI.
The difference remained evident at Day 42, when observed complete healing rates reached 82% among patients treated with HOVILPRI and 42% among those receiving the comparison treatments.
The trial also reported fewer adverse reactions among patients receiving HOVILPRI. Adverse reactions occurred in 22% of patients in the HOVILPRI group, compared with 54% in the investigator’s choice group. Treatment discontinuations due to adverse drug reactions were reported in 2% of patients receiving HOVILPRI and 20% of those receiving alternative treatments. Headache was the most common adverse reaction reported with HOVILPRI.
“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, chief executive officer of Asahi Kasei Therapeutics in the US and Europe.
HOVILPRI was developed by AiCuris Anti-infective Cures, which is now part of Asahi Kasei Therapeutics. The medicine belongs to a class of drugs called helicase-primase inhibitors. It works by targeting proteins that the herpes virus needs to copy its genetic material and reproduce. This approach differs from that used by commonly prescribed antiviral medicines and may help treat infections that no longer respond to standard therapies.
Herpes simplex virus can cause painful sores and lesions on the skin and mucous membranes. While infections may be mild in people with healthy immune systems, they can become more severe and persistent in immunocompromised patients, including people who have undergone organ or stem cell transplants, those living with HIV and patients receiving treatment for cancer.
For these patients, persistent HSV infections can be difficult to manage. Some alternative treatments require intravenous administration, adding to the burden of care. As an oral medicine, HOVILPRI offers a non-intravenous option for eligible adults whose infections have not responded to standard treatment.
Genovefa Papanicolaou, an infectious disease specialist at Memorial Sloan Kettering Cancer Center and an investigator in the PRIOH-1 trial, said refractory HSV infections can be prolonged and painful for patients with weakened immune systems, while existing intravenous treatment options can carry significant risks.
HOVILPRI received Fast Track and Breakthrough Therapy designations from the FDA, and its application was granted Priority Review. Asahi Kasei expects the medicine to become available in the United States before the end of 2026.
The approval expands treatment options for immunocompromised adults facing persistent HSV infections. Further clinical use will help build experience with the medicine, including its safety and effectiveness in eligible patients.