FDA Approves Pritelivir for Refractory HSV in Immunocompromised Adults

The FDA has approved pritelivir (Hovilpri; Asahi Kasei Therapeutics) tablets for mucocutaneous herpes simplex virus (HSV) lesions refractory to standard antiviral treatment in immunocompromised adults.¹ The indication covers lesions with or without documented resistance to acyclovir, valacyclovir, or famciclovir, according to a company announcement.

Pritelivir is a helicase-primase inhibitor, a mechanism distinct from nucleoside analogues, which require activation by viral thymidine kinase.¹ The agent is active against HSV-1 and HSV-2, including strains resistant to nucleoside analogues and foscarnet, the company said.¹ Aicuris developed the drug, and the FDA had granted the application priority review.²

Genovefa Papanicolaou, MD, clinical director of the infectious disease service at Memorial Sloan Kettering Cancer Center and a PRIOH-1 investigator, said pritelivir showed superior lesion healing compared with the investigator’s choice through day 28, according to the announcement.¹ “In patients with blood cancers or those who have undergone stem cell transplantation, refractory HSV infections can be prolonged, painful, and difficult to treat, while available intravenous treatments carry substantial risks,” she said.

How did pritelivir perform against the investigator’s choice in PRIOH-1?

Approval rests on part C of PRIOH-1 (NCT03073967), a randomized, open-label, comparator-controlled phase 3 superiority trial.¹ Investigators randomized and treated 101 immunocompromised adults with mucocutaneous HSV lesions refractory to standard therapy.¹ Participants in the pritelivir arm received 400 mg on day 1, then 100 mg once daily for up to 28 days, extended to 42 days if lesions continued to improve.¹

The comparator arm received the investigator’s choice of intravenous foscarnet, intravenous or topical cidofovir, or 5% topical imiquimod.¹ The primary end point was complete healing of all lesions by day 28. Healing occurred in 63% of patients receiving pritelivir versus 34% receiving investigator's choice, an adjusted difference of 28.4% (95% CI, 9.6-47.3; P = .0047).¹

Lesion response through day 42 reached 82% with pritelivir versus 42% with investigator's choice, an adjusted difference of 40.0% (95% CI, 22.7-57.7).¹ Contagion previously reported phase 3 results for pritelivir in this population.³

What safety signals and drug interactions accompany pritelivir?

Adverse reactions occurred in 22% of patients receiving pritelivir compared with 54% of those receiving investigator's choice.¹ Discontinuations due to adverse reactions were 2% versus 20%, respectively.¹ Headache was the most common adverse reaction, reported in 6% of the pritelivir group and 4% of the comparator group.¹

Acid-reducing agents may lower pritelivir exposure and reduce effectiveness, according to the announcement.¹ Clinicians should avoid esomeprazole and rabeprazole and limit omeprazole or lansoprazole to 20 mg daily or less and pantoprazole to 40 mg daily or less.¹ Patients should take pritelivir at least 2 hours before or 12 hours after H2-receptor antagonists and at least 2 hours before or after antacids.¹

Pritelivir also inhibits breast cancer resistance protein (BCRP), which may raise levels of BCRP substrate drugs and increase their risk of adverse reactions.¹ The announcement did not describe a boxed warning.¹

"HOVILPRI offers a new oral treatment option for adult patients with a persistent, difficult-to-treat disease," Stacy Wheeler, chief executive officer of Asahi Kasei Therapeutics in the US and Europe, said in a statement. Carl Kraus, chief medical officer of Asahi Kasei Therapeutics, described refractory HSV as a serious clinical challenge for immunocompromised adults with limited treatment options.¹

Refractory HSV in immunocompromised adults has carried limited treatment options, and intravenous foscarnet and cidofovir were among the comparators used in the trial.¹ Asahi Kasei expects pritelivir to become available in the US before the end of 2026.¹

References

1. 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. News release. Business Wire. October 9, 2026. https://www.businesswire.com/news/home/20261009917279/en/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

2. Aicuris receives FDA priority review for pritelivir NDA and presents new phase 3 data at ESCMID 2026. News release. April 2026.https://www.aicuris.com/press-release/aicuris-receives-fda-priority-review-for-pritelivir-nda-and-presents-new-phase-3-data-at-escmid-2026/

3. Pritelivir improves outcomes in immunocompromised patients with refractory herpes simplex virus. Contagion. February 6, 2026. https://www.contagionlive.com/view/pritelivir-improves-outcomes-in-immunocompromised-patients-with-refractory-herpes-simplex-virus