EXPRESS: Renal Health in Cats with Feline Infectious Peritonitis treated with GS-441524: Baseline Findings and Longitudinal Effects.

ObjectivesGS-441524 is effective against feline infectious peritonitis (FIP), but potential renal toxicity remains debated. Renal health was assessed in cats with FIP undergoing antiviral treatment.MethodsCats with confirmed FIP (n = 80) receiving oral GS-441524 for 42 days were assessed before (day 1; D1), during (D7, D42), and after treatment (D84, D183). Assessments included urine specific gravity (USG), urine protein:creatinine ratio (UPC), urinary cystatin B (uCysB), urine protein electrophoresis, serum creatinine, urea and symmetric dimethylarginine (SDMA).The term potential renal dysfunction was used for cats fulfilling the following criteria: creatinine >140 µmol/l or SDMA ≥ 18 µg/dl and USG <1.035. Serum amyloid A (SAA) and alpha-1-acid glycoprotein (AGP) were assessed in serum, feline coronavirus (FCoV) RNA in blood and urine (D1-D42).ResultsAt baseline, 97.5% of cats had creatinine concentrations <140 µmol/l; by D183, 23.8% exceeded this threshold (D1-D183: PD <0.0001). Potential renal dysfunction criteria were met in 2.5% of cats at baseline and 8.8% at D183. In contrast, uCysB was increased in 83.8% of cats at D1 and declined during treatment (D1-D183: PD <0.0001). Cats with uCysB >100 ng/ml had higher UPC values (PMWU <0.0001). Most cats had elevated AGP and SAA at baseline, which normalised during treatment (D1-D42: PD <0.0001). Proteinuria (UPC >0.2) was present in 91.3% on D1 and 3.8% on D183; urine protein electrophoresis at D1 revealed predominantly tubular and mixed patterns. Urine was more frequently FCoV RNA-positive than blood on D1 (68.8%/61.3%), but not on D7 (16.3%/45.0%).Conclusions and relevanceTreatment reversed FIP-associated renal abnormalities and inflammation observed at baseline. A small subset of cats met criteria compatible with potential renal dysfunction during the study. Whether these findings reflect delayed FIP-related renal insults or adverse antiviral effects remains unknown but indicate that treatment should not be extended unnecessarily.