Legal treatment of feline infectious peritonitis in the Netherlands.

ObjectivesThe study aimed to assess the clinical efficacy, safety and outcomes of legally prescribed and compounded GS-441524, with or without prior remdesivir, in cats with confirmed or highly suspected feline infectious peritonitis (FIP) in the Netherlands. A standardised diagnostic and treatment protocol was used to evaluate clinical response, adverse effects and prognostic factors.MethodsThis prospective, multicentre study included 127 client-owned cats with FIP, enrolled between June and November 2023 from three Dutch veterinary clinics. Diagnosis followed American Association of Feline Practitioners (AAFP)/EveryCat guidelines, incorporating clinical findings, laboratory data, imaging, cytology and RT-qPCR performed on either fine-needle aspirates or effusion. Cats were treated for a minimum of 12 weeks with oral GS-441524, with some initially receiving intravenous remdesivir before transitioning to oral therapy. Dosing was based on disease form (effusive, non-effusive, ocular, neurological). Follow-up included physical examinations and clinicopathological monitoring. Descriptive statistics, Kaplan-Meier survival analysis and Cox regression were used for data analysis.ResultsOf the 127 cats, 55.9% had effusive, 19.7% non-effusive, 16.5% ocular and 7.9% neurological FIP; 21.3% showed mixed forms. Most cats were aged under 2 years (87.4%), male (77.2%) and purebred (60.6%). Common clinical signs included lethargy (93%) and inappetence (83%). Overall survival was 78%. Ocular FIP had the highest survival (100%), while neurological FIP had the lowest (60%). Elevated serum bilirubin and creatinine concentrations at presentation were associated with reduced survival. Adverse effects were generally mild and transient, with vomiting (33%) and diarrhoea (29%) most commonly reported.Conclusions and relevanceThis study confirms that GS-441524, with or without prior remdesivir, is an effective and well-tolerated treatment for naturally occurring FIP. Clinical improvement was typically rapid; resolution of laboratory abnormalities took longer. These findings support the legal use of GS-441524 in feline practice and highlight the need for further research to refine treatment protocols.