Development and Physicochemical Stability of an Oral GS‐441524 Suspension for Weight‐Adjusted Treatment of Feline Infectious Peritonitis

BACKGROUND: GS-441524 is a key antiviral agent for the treatment of feline infectious peritonitis (FIP), yet no authorized veterinary medicinal product is currently available. OBJECTIVES: To provide a quality-assured alternative to unregulated products, we developed a 50 mg/mL oral suspension and evaluated its physicochemical stability. METHODS: Three independent batches were prepared using Syrspend SF pH 4.0 and a veterinary flavouring agent. Stability was assessed at 5°C, 25°C/60% RH and 40°C/75% RH (transport simulation) over 12 weeks. In-use stability was evaluated for 28 days following repeated withdrawals. Stability was defined as maintenance of drug concentration within 90%-110% of initial values (45-55 mg/mL), pH 3.5-4.5 and relative density 1.02-1.04 g/mL. RESULTS: All batches remained within predefined acceptance limits under all conditions. The formulation, therefore enables accurate oral dosing of GS-441524 for weight-adjusted therapy and provides a regulated alternative to unlicensed products. CONCLUSIONS: These findings support the suitability of the formulation as an extemporaneously compounded preparation under veterinary supervision. Pharmacokinetic and clinical performance were not assessed and should be addressed in future studies to further substantiate therapeutic use.