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 Announces FDA Approval of HOVILPRI® (pritelivir) Tablets for Mucocutaneous HSV Lesions Refractory (With or Without Resistance) to Standard Antiviral Treatment in Immunocompromised Adults
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HOVILPRI® (pritelivir), a novel oral helicase-primase inhibitor represents the first FDA approved HSV therapy with a novel mechanism of action in nearly 30 years.1-3
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Approval is supported by results from the pivotal Phase 3 PRIOH-1 trial, in which HOVILPRI demonstrated statistically superior complete lesion healing up to day 28. By Day 28, 63% of HOVILPRI-treated participants achieved complete lesion healing compared with 34% of participants receiving Investigator’s Choice treatment, corresponding to an adjusted treatment difference of 28.4% (95% CI: 9.6, 47.3; p=0.0047).1,4
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As an oral therapy, HOVILPRI provides a non-intravenous treatment option for eligible immunocompromised adult patients with refractory (with or without resistance) HSV infection.1
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Pritelivir was granted Fast Track designation by the FDA along with Breakthrough Therapy designation and the New Drug Application received Priority Review.5,6
TOKYO–(BUSINESS WIRE)–Asahi Kasei Therapeutics, Inc., the global specialty pharmaceutical business of Tokyo-based Asahi Kasei, with U.S. and European business headquarters in Cary, North Carolina, today announced that the U.S. Food and Drug Administration (FDA) has approved HOVILPRI® (pritelivir) 100 mg tablets for the treatment of mucocutaneous lesions caused by herpes simplex virus (HSV) infection that is refractory (with or without documented resistance) to treatment with acyclovir, valacyclovir, or famciclovir in immunocompromised adults. HOVILPRI, a novel helicase-primase inhibitor, was developed by AiCuris Anti-infective Cures AG, which is now a part of Asahi Kasei Therapeutics.1,2
“Today’s approval delivers the first FDA-approved treatment for refractory mucocutaneous HSV lesions with a novel mechanism of action in nearly 30 years and marks an important advancement for immunocompromised adults,” said Stacy Wheeler, Chief Executive Officer of Asahi Kasei Therapeutics in the U.S. and Europe. “HOVILPRI offers a new oral treatment option for adult patients with a persistent, difficult-to-treat disease.”1,3,7-10
In immunocompetent adults, HSV infection is often asymptomatic or associated with mild disease. In immunocompromised adults, including hematopoietic stem cell and solid organ transplant recipients, people living with HIV, and patients with malignancies or autoimmune and inflammatory conditions, HSV infection can occur more frequently and may be more severe. Refractory HSV infection can result in prolonged and difficult-to-treat mucocutaneous disease.7-10 Because nucleoside analogue therapies such as acyclovir require activation by the viral thymidine kinase (TK) enzyme, mutations in TK can reduce susceptibility to these treatments in some patients.2,9 When HSV infection does not improve with nucleoside analogue therapy, available treatment options have often required intravenous administration and may present additional treatment-management challenges for patients and healthcare teams.8-10 HOVILPRI is a helicase-primase inhibitor with a mechanism of action distinct from nucleoside analogue therapies.1,2
The approval is supported by results from PRIOH-1 Part C, the pivotal Phase 3 randomized, open-label, comparator-controlled superiority trial in immunocompromised adults with mucocutaneous HSV infection that was refractory, with or without documented resistance, to acyclovir, valacyclovir, or famciclovir. The trial met its primary efficacy endpoint, demonstrating superiority of HOVILPRI over Investigator’s Choice treatment, after up to 28 days of treatment. By Day 28, HOVILPRI achieved a significantly higher rate of complete lesion healing vs Investigator’s Choice (63% vs 34% respectively, corresponding to an adjusted treatment difference of 28.4% (95% CI: 9.6, 47.3; p=0.0047). Up to day 42, the observed response rates were 82% for HOVILPRI and 42% for Investigator’s Choice treatment, corresponding to an adjusted treatment difference of 40.0% (95% CI: 22.7, 57.7).1,4
In Part C of the pivotal Phase 3 PRIOH-1 trial, adverse reactions were reported less frequently in participants treated with HOVILPRI compared with Investigator’s Choice treatment (22% vs. 54%). Discontinuations due to adverse drug reactions were also less frequent with HOVILPRI compared with Investigator’s Choice treatment (2% vs. 20%). The most common adverse reaction was headache, occurring in 6% of patients taking HOVILPRI and 4% of patients taking Investigators Choice.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,” said Genovefa Papanicolaou, MD, Clinical Director of Infectious Disease Service at Memorial Sloan Kettering Cancer Center and Professor at Weill Cornell College of Medicine, and a PRIOH-1 investigator. “In PRIOH-1, pritelivir demonstrated superior lesion healing compared with Investigator’s Choice treatment up to day 28.”1,4,7-10
“Refractory HSV can be a serious clinical challenge for immunocompromised adults, a population with limited treatment options,” said Carl Kraus, Chief Medical Officer at Asahi Kasei Therapeutics. “The approval of HOVILPRI reflects years of clinical research in refractory HSV and reinforces our commitment to advancing scientifically differentiated medicines for patients whose conditions remain difficult to treat. We are grateful to the patients, investigators, clinical teams, and scientific community whose contributions made this milestone possible.”1,4,7-10
HOVILPRI is expected to be available in the United States before the end of 2026. U.S. Healthcare providers can learn more about HOVILPRI at www.hovilprihcp.com.
About the PRIOH-1 Trial
PRIOH-1 (NCT03073967 / Eudra-CT 2023-510088-37-00) is a global, controlled, open-label, comparative trial evaluating pritelivir in immunocompromised adults with refractory or resistant HSV infection. The registrational Phase 3 portion (Part C) randomized and treated 101 immunocompromised adults with mucocutaneous HSV infection that was refractory with or without documented resistance to acyclovir, valacyclovir, or famciclovir. This included hematopoietic cell and solid organ transplant recipients, patients with malignancies, autoimmune or inflammatory disorders, and people living with HIV. Participants received either oral pritelivir (400 mg loading dose on Day 1 followed by 100 mg once daily) or Investigator’s Choice treatment (IV foscarnet, IV/topical cidofovir, or 5% topical imiquimod) for up to 28 days, with treatment extended to 42 days if lesions were improving. Pritelivir met its primary endpoint demonstrating statistically significant superiority in lesion healing up to Day 28 compared with Investigator’s Choice treatment.1,4
About Herpes Simplex Virus
Herpes Simplex Virus (HSV) includes two types, HSV-1 and HSV-2, both of which cause lifelong infections; there is no cure. HSV-1 most commonly causes labial herpes, while HSV-2 is the primary cause of genital herpes. Although many people with HSV infection never develop symptoms, the virus can reactivate to cause recurrent, painful lesions and may cause complications in certain cases.11-12 HSV represents a substantial global public health burden: an estimated 3.8 billion people under the age of 50 (64% of the global population) were infected with HSV-1 in 2020, and approximately 520 million people aged 15 to 49 were living with HSV-2.11 The disease burden is particularly high in immunocompromised patients, whose weakened immune systems leave them at increased risk of more frequent, more severe, and treatment-refractory HSV infections.7,9-10
About HOVILPRI (pritelivir)
HOVILPRI is an orally administered HSV helicase-primase inhibitor indicated for the treatment of mucocutaneous lesions caused by HSV infection that is refractory, with or without documented resistance, to acyclovir, valacyclovir, or famciclovir in immunocompromised adults. HOVILPRI is active against both HSV-1 and HSV-2, including strains resistant to nucleoside analogs and foscarnet. In the pivotal Phase 3 PRIOH-1 trial, HOVILPRI demonstrated statistically significant superiority in lesion healing up to day 28 compared to Investigator’s Choice treatment. The most common adverse reaction reported with HOVILPRI was headache.1-2,4
INDICATION AND IMPORTANT SAFETY INFORMATION FOR US AUDIENCE
Indication
HOVILPRI (pritelivir) tablets is indicated in immunocompromised adults for the treatment of mucocutaneous lesions caused by herpes simplex virus (HSV) infection that is refractory (with or without documented resistance) to treatment with acyclovir, valacyclovir, or famciclovir.
Important Safety Information
Warnings and Precautions
Drug Interactions With Acid-reducing Agents: Concomitant use of HOVILPRI with certain acid-reducing agents may reduce pritelivir exposure, potentially resulting in reduced therapeutic effect and development of resistance. Avoid concomitant use with certain proton pump inhibitors, and stagger concomitant use with H2-receptor antagonists and antacids.
Adverse Reactions: In clinical studies, the adverse reaction (all grades) occurring in more than 5% of participants receiving HOVILPRI was headache, which occurred in 6% and 4% of the HOVILPRI and Investigator’s Choice participants, respectively.
Drug Interactions:
Pritelivir is a breast cancer resistance protein (BCRP) inhibitor. Co-administration of HOVILPRI with a BCRP substrate may increase the plasma concentrations of the BCRP substrate, which may increase the risk of adverse reactions.
Concomitant use of acid-reducing agents may elevate gastric pH and decrease the systemic bioavailability of HOVILPRI, which may reduce its effectiveness or cause drug resistance to HOVILPRI. Avoid concomitant use with esomeprazole or rabeprazole. Avoid concomitant use with omeprazole or lansoprazole at daily doses above 20 mg, or with pantoprazole at daily doses above 40 mg. Take HOVILPRI at least 2 hours before or 12 hours after H2-receptor antagonists. Take HOVILPRI at least 2 hours before or 2 hours after antacids.
Please see full Prescribing Information at https://www.hovilprihcp.com/pdf/prescribing-information.pdf.
About Asahi Kasei Therapeutics
Asahi Kasei Therapeutics is the global specialty pharmaceutical business of Tokyo-based Asahi Kasei. We are identifying, developing and commercializing innovative medicines for diseases with significant unmet medical needs. Drawing upon our strong heritage of scientific innovation, we are expanding therapeutic options and helping to positively impact health in immunology, nephrology, transplantation, and infectious diseases. For more information, visit: https://www.aktx.com.
About Asahi Kasei
Asahi Kasei is a diversified global company that contributes to life and living for people around the world. Since its foundation in 1922, with businesses in ammonia and cellulose fiber, Asahi Kasei has consistently grown through proactive portfolio transformation to meet the evolving needs of every age. With 50,000 employees worldwide, the company contributes to sustainability by providing solutions to the world’s challenges across its three business sectors: Healthcare, Homes, and Material. For more information, visit https://www.asahi-kasei.com/.
Asahi Kasei positions Pharmaceuticals as a First Priority business in its medium-term management plan, emphasizing value creation by expanding its research and development activities globally to deliver innovative therapeutic options worldwide.
References:
1. HOVILPRI (pritelivir) tablets. Prescribing information. Asahi Kasei Therapeutics, Inc.; 2026.
2. Birkmann A et al. J Med Chem. 2022;65(20):13614-13628. doi:10.1021/acs.jmedchem.2c00668
3. Birkmann A, Saunders R. Antiviral Res. 2025;237:106152. doi:10.1016/j.antiviral.2025.106152
4. Papanicolaou GA et al. Oral late-breaker presented at: Tandem Meetings; February 4-7, 2026; Salt Lake City, Utah.
5. AiCuris Anti-infective Cures AG. FDA Breakthrough Therapy designation and Priority Review correspondence. Data on file.
6. AiCuris Anti-infective Cures AG. Aicuris Receives FDA Priority Review for Pritelivir NDA and Presents New Phase 3 Data at ESCMID 2026. Published April 16, 2026.
7. Shafat T et al. Clin Microbiol Infect. 2025;31(5):761-772. doi:10.1016/j.cmi.2025.01.033
8. Hammond SP et al. Open Forum Infect Dis. 2024;11(3):ofae046. doi:10.1093/ofid/ofae046
9. Sallée L, Boutolleau D. Rev Med Virol. 2024;34(5):e2574. doi:10.1002/rmv.2574
10. Chemaly RF et al. Clin Infect Dis. 2025;81(3):593-601. doi:10.1093/cid/ciae638
11. Harfouche M et al. Sex Transm Infect. 2025;101(4):214-222. doi:10.1136/sextrans-2024-056307
12. Workowski KA et al. MMWR Recomm Rep. 2021;70(4):1-187. doi:10.15585/mmwr.rr7004a1
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Contacts
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Asahi Kasei Therapeutics
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