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GS-441524 is an adenosine nucleoside antiviral demonstrating significant efficacy in the treatment of feline infectious peritonitis (FIP), an otherwise fatal illness, resulting from infection with feline coronavirus. However, following the emergence of COVID-19, veterinary development was halted, and Gilead pursued clinical development of a GS-441524 pro-drug, resulting in the approval of Remdesivir under an FDA emergency use authorization. Despite lack of regulatory approval, GS-441524 is available without a prescription through various unlicensed online distributors and is commonly purchased by pet owners for the treatment of FIP. Herein, we report data obtained from the analytical characterization of two feline renal calculi, demonstrating the propensity for GS-441524 to cause renal toxicity through drug-induced crystal nephropathy in vivo. As definitive diagnosis of drug-induced crystal nephropathy requires confirmation of the lithogenic material to accurately attribute a mechanism of toxicity, renal stone composition and crystalline matrix were characterized using ultra-performance liquid chromatography photodiode array detection (UPLC-PDA), ultra-performance liquid chromatography mass spectrometry (LCMS), nuclear magnetic resonance (NMR) spectroscopy, X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). This work serves to provide the first analytical confirmation of GS-441524-induced crystal nephropathy in an effort to support toxicologic identification of adverse renal effects caused by administration of GS-441524 or any pro-drug thereof. [Display omitted] • This work describes the first analytical confirmation of GS-441524 toxicity in vivo. • Samples were obtained from felines with suspected GS-441524 crystal nephropathy. • Renal stones were characterized by UPLC-PDA, LCMS, NMR, XRD, and FTIR. • Consistent spectral results were observed across all analytical techniques. [ABSTRACT FROM AUTHOR]

Feline infectious peritonitis (FIP) historically has been a fatal disease in cats. Recent unlicensed use of antiviral medication has been shown to markedly improve survival of this infection. An 8‐month‐old female spayed domestic short‐haired cat undergoing treatment for presumptive FIP with the antiviral nucleoside analog GS‐441524 developed acute progressive azotemia. Abdominal ultrasound examination identified multifocal urolithiasis including renal, ureteral, and cystic calculi. Unilateral ureteral obstruction progressed to suspected bilateral ureteral obstruction and subcutaneous ureteral bypass (SUB) was performed along with urolith removal and submission for analysis. A 2‐year‐old male neutered domestic medium‐haired cat undergoing treatment for confirmed FIP with GS‐441524 developed dysuria (weak urine stream, urinary incontinence, and difficulty expressing the urinary bladder). This cat also was diagnosed sonographically with multifocal urolithiasis requiring temporary tube cystostomy after cystotomy and urolith removal. In both cases, initial urolith analysis showed unidentified material. Additional testing confirmed the calculi in both cats to be 98% consistent with GS‐441524. Additional clinical studies are required to determine best screening practices for cats presented for urolithiasis during treatment with GS‐441524. [ABSTRACT FROM AUTHOR]