Treatment of feline infectious peritonitis in cats with molnupiravir: clinical observations and outcomes for 54 cases

Objective To evaluate the clinical applications and treatment outcomes using molnupiravir for the treatment of naturally occurring feline infectious peritonitis virus (FIPv). Methods Ninety‐two client‐owned cats with confirmed or presumptive FIP were retrospectively recruited from 35 veterinary practices, primarily in Australia, between February 2023 and March 2024. Cats were categorised based on treatment received: Cohort A: Molnupiravir treatment: monotherapy, maintenance or rescue therapy; Cohort B: Remdesivir and/or GS‐441524 treatment. Seventy‐eight cats were enrolled. Molnupiravir was administered orally for a median of 84 days, at a median dose of 13.3 mg/kg BID. Remission was defined as the resolution of FIP‐related signs with (i) normalisation of serum globulin concentrations and A:G ratio (≥0.6), or (ii) sustained clinical remission for at least 100 days after stopping anti‐viral therapy. Cure rate was defined as the percentage of cats achieving sustained remission, without requiring rescue therapy or experiencing a relapsed disease. Results Molnupiravir monotherapy resulted in a cure rate of 72% (13/18) while molnupiravir maintenance therapy achieved a cure rate of 86% (25/29), and molnupiravir utilised as a rescue therapy achieved a cure rate of 100% (7/7). Treatment with remdesivir/GS‐441524 resulted in a cure rate of 71% (17/24 cats). Survival analysis revealed no difference in outcomes between cats treated with molnupiravir monotherapy and those treated with remdesivir/GS‐441524. Adverse events associated with molnupiravir therapy included neutropenia, and transient elevations in hepatic enzymes. Conclusion Molnupiravir demonstrated comparable survival outcomes to remdesivir/GS‐441524 for treating FIP and serves as an accessible, effective option across various presentations, including ocular and neurologic forms.