FDA Approves Pritelivir For Resistant Herpes In Immunocompromised
The FDA has approved pritelivir tablets for immunocompromised adults with herpes simplex virus lesions that have not responded to standard antiviral treatments.
The FDA has approved pritelivir tablets for immunocompromised adults with mucocutaneous herpes simplex virus lesions unresponsive to standard antivirals. The agency approved the drug, branded as Hovilpri and developed by Asahi Kasei Therapeutics, on October 9, 2026. It is indicated for immunocompromised patients whose lesions caused by HSV infection have not responded to acyclovir, valacyclovir, or famciclovir.
How it works and who it helps
Pritelivir inhibits viral replication through a novel mechanism. It is a helicase-primase inhibitor, which blocks a separate set of viral proteins the virus needs to copy its genetic material. This mechanism does not depend on thymidine kinase, making it effective against HSV-1 and HSV-2 strains resistant to nucleoside analogue- and foscarnet-based treatments.
The approval supports patients with refractory infection, with or without documented antiviral resistance. It is intended for those whose persistent infections can complicate cancer treatment or transplantation care. Participants in the supporting trial had conditions including hematologic malignancies or disorders, hematopoietic stem-cell transplants, autoimmune or inflammatory diseases, nonhematologic malignancies, solid-organ transplants, or HIV infection.
Clinical trial results
Approval was based on the open-label, phase III PRIOH-1 trial. It compared once-daily pritelivir versus investigators' choice of foscarnet, cidofovir, or imiquimod in 101 immunocompromised patients with mucocutaneous HSV infection unresponsive to conventional therapy. Patients received treatment for up to 28 days, with an option to continue to 42 days if lesions were improving.
The primary endpoint was complete healing of all lesions during the first 28 days. Complete lesion healing occurred in 63% of pritelivir recipients, compared to 34% of those receiving investigator-selected therapy. The adjusted treatment difference was 28.4 percentage points. By day 42, 82% of the pritelivir arm had fully healed lesions versus 42% of the control arm.
Adverse event rates were lower in pritelivir-treated patients (22%) than in controls (54%). Treatment discontinuation rates were 2% for pritelivir versus 20% for controls.
| Trial Measure | Pritelivir Group | Control Group |
|---|---|---|
| Lesions healed by day 28 | 63% | 34% |
| Lesions healed by day 42 | 82% | 42% |
| Adverse event rate | 22% | 54% |
| Treatment discontinuation rate | 2% | 20% |
Safety and use considerations
Pritelivir showed lower adverse event and discontinuation rates than control therapies. Headache was the most common adverse reaction, occurring in 6% of pritelivir-treated patients and 4% of controls.
The drug label includes important warnings about drug interactions. Acid-reducing agents can reduce pritelivir exposure. Concomitant use of the proton pump inhibitors esomeprazole and rabeprazole should be avoided altogether. Use with omeprazole and lansoprazole at higher doses is also not recommended. Concomitant use with H2-receptor antagonists like ranitidine and famotidine should be staggered; pritelivir should be taken at least 2 hours before or 12 hours after these drugs. It should also be taken at least 2 hours before or after antacids. Also, pritelivir inhibits breast cancer resistance protein, which may increase exposure to other medications that are substrates of this transporter. Pharmacists must review medications due to these interactions.
Context for immunocompromised patients
Herpes simplex virus causes a lifelong infection with recurrent mucocutaneous lesions on areas like the lips, nostrils, eyes, and genitals. Outbreaks occur particularly in patients with compromised immune systems. While antiviral medicines control outbreaks, they do not eliminate the latent virus.
Resistant strains severely limit treatment options. CDC guidance states that acyclovir-resistant HSV strains are also resistant to valacyclovir, and most are resistant to famciclovir. The CDC recommends infectious disease consultation for suspected resistant infection and identifies intravenous foscarnet as a treatment. However, foscarnet and cidofovir carry significant risks. They are associated with nephrotoxicity and require intensive laboratory monitoring. A retrospective study of foscarnet found electrolyte disturbances occurred in 65% of treatment episodes and kidney dysfunction in 42%. Adverse events led to drug discontinuation in 32% of episodes.
Patients should consult their healthcare provider to determine if pritelivir is appropriate for their condition, especially if they are taking acid-reducing medications.
