Treatment duration: evidence for shorter courses and when they need longer

Overview

Historically, a 84-day (12-week) course of antiviral treatment with GS-441524 was the standard approach for treating cats with feline infectious peritonitis (FIP), largely based on the protocols used in early GS-441524 studies rather than on evidence establishing 84 days as the minimum duration required for cure. Early studies demonstrated excellent efficacy with prolonged treatment, but relapses—particularly neurological relapses—were observed in some cats and contributed to a cautious approach to treatment duration.More recent evidence challenges the need for routine 84-day therapy.

A prospective randomized controlled study compared 42 versus 84 days of oral GS-441524 (15 mg/kg q24h) in 40 cats with FIP with effusion. Nineteen of 20 cats in each treatment group recovered, and all surviving cats remained in complete remission throughout follow-up to day 168. No clinically relevant differences in response, laboratory variables, or viral load were detected between treatment groups. These findings provide strong evidence that 42 days of treatment can be sufficient in cats that have responded appropriately and are clinically stable by day 42. Moreover, a large bi-center study evaluated efficacy of a 42-day oral GS-441524 treatment protocol across a broader population, including various clinical manifestations of FIP and cats with retroviral co-infections. All cats received oral GS-441524 (BOVA, UK) at 15 mg/kg, q24h for 42 days (11 cats received initial intravenous remdesivir before transitioning to GS-441524).

Rapid improvement of clinical and laboratory parameters, including acute-phase-proteins was observed. Treatment success and survival rates were high. Confirmed relapse cases only occurred in few cats. This new study demonstrated that a 42-day treatment duration is sufficient for all manifestations of FIP and in cats with retroviral co-infections. Still, treatment duration should be response-guided rather than predetermined. A 42-day course is a reasonable evidence-based option when clinical signs have resolved and relevant clinicopathological abnormalities have substantially normalized. Treatment should be continued beyond 42 days when there is persistent or recurrent disease activity, incomplete clinical response, or unresolved abnormalities attributable to FIP. Importantly, failure to respond as expected should prompt reassessment of diagnosis, dose, drug exposure, and potential complications, rather than simply extending treatment automatically.

Learning outcomes:

By the end of this webinar, participants should be able to:

Explain the evidence supporting a 42-day course of oral GS-441524 in cats with FIP.
Apply appropriate monitoring to cats receiving GS-441524 treatment.Identify cats in which treatment can be safely discontinued after 42 days, based on clinical response and appropriate monitoring.
Recognize clinical scenarios in which treatment beyond 42 days should be considered, including incomplete clinical or laboratory response.
Differentiate between treatment duration and antiviral dose as separate determinants of therapeutic success, particularly in cats with neurological and/or ocular involvement.Apply an individualized, response-guided approach to treatment duration rather than routinely prescribe a fixed 84-day course for every cat with FIP.