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

Objective: To clarify the clinical course during molnupiravir treatment for feline infectious peritonitis (FIP).

Animals and procedure: Cats diagnosed with FIP and treated with molnupiravir at Hokkaido University Veterinary Teaching Hospital (Sapporo, Hokkaido, Japan) were retrospectively reviewed.

Results: 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.

Conclusion and clinical relevance: Monitoring responses to molnupiravir treatment requires observing clinical signs and conducting clinicopathological evaluations, including acute-phase protein evaluation.