FDA Approves Hovilpri for Drug-Resistant Herpes Lesions

FDA approved pritelivir, sold as Hovilpri, on 9 October 2026 for adults with weakened immune systems whose herpes simplex virus (HSV) lesions did not heal on acyclovir, valacyclovir or famciclovir — the three nucleoside-analogue antivirals that have anchored HSV treatment for decades and that, critically, share a single resistance pathway. Pritelivir works differently, which is the entire point: AiCuris and Asahi Kasei are calling it the first new mechanism for HSV treatment in more than twenty years.

The resistance problem this was built for

Acyclovir, valacyclovir and famciclovir are all nucleoside analogues: they get activated inside infected cells and then jam the same viral DNA polymerase. That shared mechanism is efficient for drug development but fragile for patients — a mutation that defeats one of the three frequently defeats all of them. For most people, that rarely matters: a healthy immune system clears HSV lesions even when antiviral drugs underperform. For immunocompromised patients — transplant recipients, people on long-term immunosuppression, certain cancer patients — lesions can persist, spread and resist every nucleoside analogue on the shelf, with intravenous foscarnet as the fallback of last resort and its own toxicity profile.

Pritelivir is a helicase-primase inhibitor. It blocks a different viral enzyme complex entirely, one not touched by the resistance mutations that defeat the nucleoside analogues. That is the clinical case for the approval: not a marginally better version of an existing drug, but a mechanistically distinct option for exactly the patients who have run out of mechanistically similar ones.

What the trial showed

The approval rests on a 101-participant trial in immunocompromised adults with HSV lesions refractory to standard antiviral therapy, with or without documented resistance. By day 28, roughly 63% of patients on pritelivir had all lesions completely healed, compared with about 34% on the comparator regimen — the kind of gap that reads as clinically meaningful in a population with no good options left. The most commonly reported side effects were headache, diarrhea, nausea, reduced appetite, vomiting and dizziness.

From priority review to approval

FDA granted pritelivir's New Drug Application priority review in April 2026, the same month Asahi Kasei completed its acquisition of AiCuris Anti-infective Cures AG, the German anti-infectives company that originated the molecule. AiCuris presented additional Phase 3 data at ESCMID Global 2026 following the priority-review grant. The approval landed ahead of the drug's fourth-quarter 2026 PDUFA target date. Asahi Kasei has pointed to roughly 15,000 U.S. patients — immunocompromised adults with HSV lesions refractory to standard antivirals — as the population the approval is meant to reach.

What it means for prescribers

For RA/QA teams and clinicians managing immunocompromised patients, Hovilpri's approval adds a genuinely new rung to the treatment ladder rather than a reformulation of an existing one. Resistance testing and treatment-history review become more consequential: a patient who has failed one nucleoside analogue has, in practical terms, likely failed the class, and pritelivir's different mechanism is the reason it can still work where foscarnet was previously the only fallback. Full prescribing information, including dosing and any boxed warnings, is expected on Hovilpri's label as it becomes available through Drugs@FDA.

Frequently asked questions

What did FDA approve on 9 October 2026?

Pritelivir, marketed as Hovilpri, an oral tablet for adults with weakened immune systems who have mucocutaneous HSV lesions that did not respond to acyclovir, valacyclovir or famciclovir.

How well did it work in the pivotal trial?

In a 101-participant trial comparing pritelivir to existing therapy for refractory HSV, roughly 63% of immunocompromised patients had all lesions fully healed by day 28, versus about 34% on the comparator arm.

Why does the mechanism matter?

Pritelivir is a helicase-primase inhibitor, a different mechanism than acyclovir, valacyclovir and famciclovir, which share a resistance pathway as nucleoside analogues. Pritelivir's different target gives clinicians an option when cross-resistance leaves no nucleoside analogue left to try.

Who developed it, and how large is the eligible population?

AiCuris, a German anti-infectives company Asahi Kasei completed acquiring in April 2026, developed pritelivir. Asahi Kasei has estimated the approval could serve roughly 15,000 patients in the U.S.