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.

Conclusions: 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.