Evaluation of the course of improvement with molnupiravir treatment for feline infectious peritonitis.

To clarify the clinical course during molnupiravir treatment for feline infectious peritonitis (FIP). Cats diagnosed with FIP and treated with molnupiravir at Hokkaido University Veterinary Teaching Hospital (Sapporo, Hokkaido, Japan) were retrospectively reviewed. Eleven cats were eligible for inclusion. Six cats had effusive FIP and 5 had non-effusive FIP. In noneffusive cases, 2 cats had neurological abnormalities at diagnosis, whereas 1 additional cat developed neurological signs during treatment. The median initial dosage of molnupiravir was 13.0 mg/kg (range: 10.0 to 15.0 mg/kg), PO, q12h. One cat died after 11 d and the remaining 10 cats completed an 84-day course of treatment. All neurological cases were given dosage increases, extended treatment duration, or both. The median final dosage of molnupiravir in non-neuro-FIP cases was 13.1 mg/kg (range: 10.0 to 15.0 mg/kg), PO, q12h, whereas dosages in neuro-FIP cases were 15.0, 15.2, and 17.2 mg/kg, PO, q12h in the 3 affected cats, respectively. In non-neurological cases, dysrexia, lethargy, and high serum amyloid A were resolved within 15 d. Total follow-up duration ranged from 175 to 362 d. No relapses were observed. Monitoring responses to molnupiravir treatment requires observing clinical signs and conducting clinicopathological evaluations, including acute-phase protein evaluation.