FDA approves pritelivir tablets to treat lesions from HSV

The FDA has approved pritelivir (Hovilpri) tablets for adults with weakened immune systems who have mucocutaneous lesions caused by herpes simplex virus (HSV) infection that did not respond to acyclovir, valacyclovir, or famciclovir. Pritelivir’s application was granted priority review, according to a news release from the federal agency delivered on October 9, 2026.

HSV infection cannot be cured, and lesions can appear on the skin or on mucosal surfaces such as the lips, nostrils, eyes, or genitals. Immunocompromised patients may experience more frequent and serious outbreaks that respond poorly to available treatments because of drug resistance or intolerance of adverse effects.¹

How was pritelivir evaluated in the PRIOH-1 trial?

Approval was based on Part C of the phase 3 PRIOH-1 trial (NCT03073967)², a randomized, open-label, comparator-controlled superiority trial of 101 immunocompromised adults. Underlying immunosuppressive conditions included hematologic malignancy or disorder, hematopoietic stem cell transplantation, HIV infection, autoimmune or inflammatory disease, nonhematologic malignancy, and solid organ transplantation.¹

In Part C, participants with acyclovir-resistant mucocutaneous HSV were randomly assigned 1:1 to oral pritelivir or investigator's choice of treatment. Pritelivir was given as a 400-mg loading dose followed by 100 mg once daily.

Comparator options, used where nationally approved, included intravenous foscarnet 40 mg/kg every 8 hours or 60 mg/kg every 12 hours, intravenous cidofovir 5 mg/kg once weekly, topical cidofovir 1% or 3% applied 2 to 4 times daily, or topical imiquimod 5% 3 times per week, according to trial data listed on ClinicalTrials.gov. Treatment continued until all lesions healed or for up to 28 days, with possible extension to a maximum of 42 days depending on clinical progress.²

Lesion healing with pritelivir vs investigator's choice

The primary endpoint was the proportion of participants with all lesions healed by day 28. Complete healing occurred in 63% of patients receiving pritelivir, compared with 34% of those receiving other medications. Headache was the most common adverse reaction according to the FDA, which stated users should see prescribing information for certain drug interactions.¹

What other patient groups does the PRIOH-1 program include?

PRIOH-1 includes several parts beyond Part C. Completed phase 2 Parts A and B evaluated pritelivir vs intravenous foscarnet in acyclovir-resistant infection and pritelivir alone in patients with foscarnet resistance or intolerance. Phase 3 Parts D and F assess pritelivir in patients with acyclovir-resistant disease who also have foscarnet resistance or intolerance, with Part D closed in June 2022. Part E evaluates pritelivir in acyclovir-susceptible mucocutaneous HSV episodes.²

Previous data presented at ESCMID 2026

In April 2026, at the time of Priority Review designation from the FDA, the manufacturer Aicuris announced new phase 3 data that were presented at the European Society of Clinical Microbiology and Infectious Diseases via a late-breaking oral presentation. Findings included, according to the manufacturer³:

• Treatment effect and response rates increased with extended treatment up to 42 days; among patients who continued therapy, 82.4% of those treated with pritelivir achieved complete lesion healing compared with 42.0% with investigator’s choice therapy (ICT), resulting in an adjusted treatment difference of 40.2% (p < 0.0001)
• Pritelivir treatment significantly reduced viral replication and viral burden, shortening the median time to undetectable HSV in lesions to 9 days compared with 21 days with ICT (p = 0.0581)
• Pritelivir demonstrated consistent treatment effects across major immunocompromised subgroups, including patients with hematological malignancies, hematopoietic stem cell and solid organ transplant recipients, and people living with HIV
• Pritelivir demonstrated a favorable safety and tolerability profile; treatment emergent adverse events (TEAEs) included renal, electrolyte and drug-related events, with a discontinuation rate substantially lower than reported under ICT (2.0% vs. 20%); the most common TEAEs reported were headache, diarrhea, nausea, decreased appetite, vomiting and dizziness with an incidence above or equal to 5%

“For immunocompromised patients with refractory HSV infections, achieving rapid lesion healing while maintaining tolerability is essential,” said Cynthia Wat, Chief Medical Officer of Aicuris, at the time of Priority Review designation. “The new 42 day data to be presented at ESCMID demonstrate that continued pritelivir treatment translated early clinical improvement into full lesion healing, while maintaining a strong antiviral response. This efficacy response is independent of the patient’s underlying immunosuppressive disease. Combined with a favorable safety profile, these results support our confidence in pritelivir’s potential to meaningfully improve outcomes in different vulnerable patient populations.”

References:

1. FDA approves drug to treat lesions caused by herpes simplex virus. News release. US Food and Drug Administration. October 9, 2026. Accessed October 9, 2026. https://www.fda.gov/drugs/news-events-human-drugs/fda-approves-drug-treat-lesions-caused-herpes-simplex-virus
2. A randomized, open label, multi-center, comparative trial, to assess the efficacy and safety of pritelivir for the treatment of acyclovir-resistant mucocutaneous HSV (herpes simplex virus) infections in immunocompromised subjects (PRIOH-1). ClinicalTrials.gov identifier: NCT03073967. Accessed October 9, 2026. https://clinicaltrials.gov/study/NCT03073967
3. Aicuris receives FDA Priority Review for pritelivir NDA and presents new phase 3 data at ASCMID 2026. Aicuris. News release. Published April 16, 2026. Accessed October 9, 2026. https://www.aicuris.com/press-release/aicuris-receives-fda-priority-review-for-pritelivir-nda-and-presents-new-phase-3-data-at-escmid-2026/