Clinical trial of molnupiravir with or without an oral immune stimulant as a first-line treatment of feline infectious peritonitis

Objectives The aim of the present study was to evaluate the efficacy of oral molnupiravir (MPV; EIDD-2801) in cats with naturally occurring feline infectious peritonitis (FIP), with a subset of cats being administered a known immune stimulant (liposome-toll-like receptor agonist complex [LTC] orally. Methods A prospective, open-label longitudinal single-center clinical trial was conducted. Cats with FIP were enrolled and treated with oral MPV (10–21 mg/kg PO q12h) for 84 days. A subset of cats (41 cats with effusive FIP) was randomized to concurrently be administered the oral immune stimulant. Cats were evaluated at 0, 4, 8 and 12 weeks followed by a 12-week observation period. Results A total of 73 cats were included in the study and 77% of the cats survived to 6 months. The median total bilirubin concentrations were significantly different ( P = 0.0007) between the survivors vs non-survivors. Relapses occurred in 12% of the cats (at 9–99 days after discontinuing treatment), and all achieved remission during a second course of treatment. Clinicopathologic features associated with FIP normalized during the study period; however, some cats showed decreased cholesterol levels and lymphocytosis during treatment. No adverse effects necessitated discontinuation of either treatment. No effects of the LTC were apparent in this study. Conclusions and relevance MPV administered at 10–21 mg/kg PO q12h for 12 weeks is well tolerated and an effective treatment (77% success) for all forms of naturally occurring FIP, with a relapse rate of 12%. These results support those of other studies showing that MPV is an effective treatment for cats diagnosed with FIP. Additional studies will be required to determine if any benefits might be derived from the LTC treatment.