Molnupiravir treatment of 18 cats with feline infectious peritonitis: A case series

BACKGROUND: Feline infectious peritonitis (FIP) is a viral disease in cats, caused by certain strains of coronavirus and has a high case fatality rate. OBJECTIVE: This case series reports the outcomes of treatment of cats with FIP using molnupiravir. ANIMALS: Eighteen cats diagnosed with FIP at the You-Me Animal Clinic, Sakura-shi, Japan between January and August 2022, and whose owners gave informed consent to this experimental treatment. METHODS: For this prospective observational study, molnupiravir tablets were compounded in-house at the You-Me Animal Clinic. Owners administered 10-20 mg/kg PO twice daily. Standard treatment duration was 84 days. RESULTS: Among 18 cats, 13 cats had effusive FIP and 5 had noneffusive FIP. Three cats had neurological or ocular signs of FIP before treatment. Four cats, all with effusive FIP, died or were euthanized within 7 days of starting treatment. The remaining 14 cats completed treatment and remained in remission at the time of writing (139-206 days after starting treatment). Elevated serum alanine transaminase (ALT) activity was found in 3 cats, all at Days 7-9, and all recovered without management. Two cats with jaundice were hospitalized, 1 during treatment (Day 37) and 1 with severe anemia at the start of treatment. CONCLUSIONS AND CLINICAL IMPORTANCE: This case series suggests that molnupiravir might be an effective and safe treatment for domestic cats with FIP at a dose of 10-20 mg/kg twice daily.