FDA Approves HOVILPRI for Refractory HSV Lesions in Immunocompromised Adults

The US Food and Drug Administration (FDA) has approved HOVILPRI® (pritelivir) 100 mg tablets for treating mucocutaneous lesions caused by herpes simplex virus (HSV) infection that are refractory, with or without documented resistance, to acyclovir, valacyclovir or famciclovir in immunocompromised adults. Asahi Kasei Therapeutics announced the approval on October 9.

Developed by AiCuris Anti-infective Cures AG, now part of Asahi Kasei Therapeutics, pritelivir is an oral helicase-primase inhibitor. The company describes HOVILPRI as the first FDA-approved treatment for refractory mucocutaneous HSV lesions with a novel mechanism of action in nearly 30 years.

Phase 3 Trial Demonstrated Superior Lesion Healing

The approval was supported by PRIOH-1 Part C (NCT03073967), a pivotal Phase 3, randomized, open-label, comparator-controlled superiority trial. The study randomized and treated 101 immunocompromised adults whose mucocutaneous HSV infection had not responded adequately to standard nucleoside analogue treatment, with or without documented antiviral resistance.

Participants received oral pritelivir as a 400 mg loading dose on Day 1 followed by 100 mg once daily, or investigator’s choice of treatment. Comparator options included intravenous foscarnet, intravenous or topical cidofovir, and 5% topical imiquimod. Treatment continued for up to 28 days and could be extended to 42 days when lesions were improving.

The primary efficacy endpoint was complete healing of all mucocutaneous lesions by Day 28. Complete healing was achieved in 63% of participants receiving pritelivir, compared with 34% receiving investigator’s choice treatment. The company reported an adjusted treatment difference of 28.4% (95% confidence interval [CI], 9.6–47.3; p=0.0047), demonstrating statistically significant superiority for pritelivir.

By Day 42, observed complete lesion-healing rates were 82% with pritelivir and 42% with investigator’s choice treatment, corresponding to an adjusted treatment difference of 40.0% (95% CI, 22.7–57.7). Treatment could be extended to 42 days in participants whose lesions were improving. These later findings provide additional information on response during extended treatment; the trial’s primary efficacy endpoint was complete healing by Day 28.

A Different Antiviral Mechanism

Pritelivir inhibits the HSV helicase-primase complex, distinguishing it from nucleoside analogue antivirals such as acyclovir, valacyclovir and famciclovir. These established treatments require activation by viral thymidine kinase, and mutations affecting this enzyme can reduce susceptibility to treatment.

HOVILPRI’s distinct mechanism provides another treatment approach for eligible immunocompromised adults whose HSV lesions are refractory to standard antiviral therapy. Its oral administration also offers a non-intravenous option in a treatment setting where comparator therapies may require intravenous administration or other treatment approaches.

The approval is relevant to immunocompromised patients, including transplant recipients and people with malignancies or other conditions affecting immune function, in whom HSV infection can be persistent and difficult to treat. The approved indication remains limited to immunocompromised adults with refractory mucocutaneous lesions following treatment with the specified standard antivirals.

Safety Findings and Treatment Considerations

In PRIOH-1 Part C, adverse reactions were reported in 22% of participants receiving pritelivir, compared with 54% receiving investigator’s choice treatment. Discontinuations due to adverse drug reactions occurred in 2% and 20% of participants, respectively.

Headache was the most commonly reported adverse reaction, occurring in 6% of pritelivir-treated participants and 4% of those receiving investigator’s choice treatment. These percentages describe the reported trial outcomes and should not be interpreted as establishing an overall safety advantage. Treatment decisions should consider the approved prescribing information and each patient’s clinical circumstances.

The company also highlighted potential drug interactions. Certain acid-reducing agents can lower pritelivir exposure and may affect treatment effectiveness, while pritelivir can increase exposure to medicines that are breast cancer resistance protein (BCRP) substrates. Healthcare professionals should consult the approved prescribing information for the specific interaction precautions and administration instructions.

Regulatory Milestone and Availability

Pritelivir received FDA Fast Track and Breakthrough Therapy designations, and its new drug application was granted Priority Review. According to the company, HOVILPRI is expected to become available in the United States before the end of 2026.

The approval introduces an oral antiviral with a distinct mechanism for immunocompromised adults with refractory mucocutaneous HSV lesions. The pivotal trial’s comparative healing results, together with the reported safety outcomes, form the principal clinical evidence supporting this treatment option.

Reference

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, Asahi Kasei Therapeutics, 09 October 2026

 Trial on Efficacy and Safety of Pritelivir Tablets for Treatment of Acyclovir-resistant Mucocutaneous HSV (Herpes Simplex Virus) Infections in Immunocompromised Subjects (PRIOH-1), ClinicalTrials.gov ID NCT03073967