Is remdesivir an effective alternative to GS-441524 for treating FIP and how does dosing differ?

Question

Accepted Answer

Remdesivir (RDV) is an effective treatment for feline infectious peritonitis (FIP) and is not merely an alternative to GS-441524 — both agents are used sequentially or in combination, with survival rates of 81–86% at 84 days across protocols incorporating either or both drugs.1245 For remdesivir, the induction dosage is 10–15 mg/kg IV or SC q24h for 4 doses, followed by a maintenance dosage of 6–15 mg/kg SC q24h continued for at least 84 days total.1 In cases of re-emergent FIP or ocular/neurological involvement, escalation to 15–20 mg/kg q24h is recommended.13 When transitioning from parenteral remdesivir to oral GS-441524, the maintenance dose of GS-441524 is 10–15 mg/kg PO q24h, continued to complete the 84-day course.1 Oral GS-441524 doses of 10–20 mg/kg/day for 84 days have also been used successfully as a standalone approach.3 The two drugs are mechanistically linked rather than interchangeable in a strict sense. Remdesivir is a prodrug that undergoes rapid hydrolysis to GS-441524 as its principal circulating metabolite; GS-441524 is then phosphorylated intracellularly to the active triphosphate form that inhibits viral RNA synthesis.17 After IV administration, conversion to GS-441524 is near-complete within minutes, providing consistent plasma exposure.7 Oral remdesivir achieves low and variable bioavailability of GS-441524, yet clinical outcomes with oral remdesivir remain favorable, suggesting plasma GS-441524 concentration is not a reliable surrogate for treatment efficacy.7 Clinical response to treatment is rapid regardless of protocol. In cats treated with combinations of IV remdesivir, SC remdesivir, and oral GS-441524, clinical response was observed in 87.5% of cats at a median of 2 days.2 Remission by day 84 was achieved in 56% of cats in one cohort using remdesivir with or without transition to oral GS-441524, with an overall 6-month survival of 86%.1 When cats survived the first 3 days of treatment, 92.8% were alive and in clinical remission at 12 w