Hovilpri (pritelivir)

Refractory mucocutaneous herpes simplex virus (HSV) infection is defined in the Hovilpri prescribing information as no clinical improvement after at least 7 days of acyclovir, valacyclovir, or famciclovir, with or without laboratory-confirmed resistance. A 2025 consensus definition describes resistant infection as refractory infection with genotypic or phenotypic evidence of decreased drug susceptibility. Reported rates differ across studies. The consensus review gives resistance rates of often 0% to 14% in hematopoietic cell transplant (HCT) recipients, 0% to 3% in solid organ transplant recipients, and 3% to 7% in advanced HIV disease. For HCT recipients, a narrative review cites small studies reporting up to 46% and a systematic review reports a median incidence of 16.1%. Laboratory-confirmed acyclovir-resistant infection occurred in 18 recipients (0.4%) among 4,028 allogeneic HCTs performed at one U.S. cancer center, and 12 of 226 HIV-positive U.S. clinic participants (5.3%) had resistant isolates. The report found no population-based U.S. estimate of refractory infection. Asahi Kasei estimates, from an internal investigation, approximately 15,000 immunocompromised people in the United States at second-line treatment.

In a cohort of 125 HCT recipients with refractory infection at 7 U.S. centers, 69 participants (55.2%) healed completely at a median of 38 days and 40 (32.0%) died on therapy. Of the 69 who healed, 27 (39.1%) had a recurrence and 22 (31.9%) died within 1 year. In a 5-center U.S. cohort, 15 of 31 foscarnet-treated episodes (48%) healed and 8 of those 15 (53%) recurred. In a single-center U.S. cohort of 18 allogeneic HCT recipients, 9 (50%) were hospitalized and 9 (50%) died within 1 year. Foscarnet in the 7-center cohort was given in a hospital or hospital-associated infusion clinic for a mean of 21.8 days. The report found no quality-of-life study using a validated instrument and no cost or length-of-stay study of this condition.

A federal HIV guideline (AI) and a 2009 HCT guideline (BI) name intravenous foscarnet as the treatment of choice, and 2007 European leukemia recommendations rate it BIII. The alternatives are intravenous cidofovir, rated CIII in the HIV and HCT guidelines, and topical imiquimod, cidofovir, trifluridine, and foscarnet, rated BIII in the HIV guideline. The foscarnet label carries a boxed warning for renal impairment and seizures and requires intravenous infusion by pump, with hydration. In the 7-center cohort, toxicity was reported during 75 of 109 foscarnet courses (68.8%), renal function abnormalities during 44 (40.4%), and discontinuation for toxicity in 33 (30.3%). A 2025 review states that, apart from two small randomized trials in people with HIV in the 1990s, treatment recommendations rest on observational studies and case reports.