Open label clinical trial of orally administered molnupiravir as a first-line treatment for naturally occurring effusive feline infectious peritonitis

Background: Before the discovery of effective antiviral drugs, feline infectious peritonitis (FIP) was a uniformly fatal disease of cats. Multiple antiviral treatments have been recognized, but optimization of treatment protocols is needed.

Objective: To evaluate the efficacy of PO molnupiravir (MPV; EIDD-2801) to treat effusive FIP.

Animals: Ten cats with naturally occurring effusive FIP and 10 historical control cats with effusive FIP treated with PO GS-441524.

Methods: A single-center, prospective, open-label longitudinal, non-inferiority trial with historical controls. Ten cats with FIP were enrolled and treated with PO MPV (10-15 mg/kg PO q12h) for 84 days. Cats were evaluated at 0, 6, and 16 weeks, and the proportion of cats in clinical remission at 16 weeks was determined. Survival and clinicopathologic features were compared with historical control cats with effusive FIP treated with PO GS-441524.

Results: Eight of the 10 cats treated with MPV survived and were in remission at 16 weeks. The 2 non-survivors died in the first 24 hours of treatment. No adverse events that necessitated discontinuation of treatment were observed. Survival of cats treated with PO MPV was non-inferior to historic control cats treated with PO GS-441524 (5/9 [55%] survived), with a difference in survival of 25% (90% confidence interval, -9.3% to 59.3%). Clinicopathologic features associated with FIP normalized during the study period, and no differences in clinicopathologic data at each study time point were observed when comparing cats treated with MPV and GS-441524.

Conclusions and clinical importance: Molnupiravir is an effective antiviral treatment for effusive FIP.