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

Objectives GS-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. Methods Cats 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). Results At 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 relevance Treatment 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.