A case series of 25 cats with effusive and non-effusive feline infectious peritonitis treated with a combination of remdesivir and GS-441524

ABSTRACT

Feline infectious peritonitis (FIP) has until recently carried a guarded prognosis due to a lack of efficacious treatments. Preliminary studies using remdesivir and GS-441524 for treatment of FIP have shown promising results. Licensing of these drugs for use in humans with COVID-19 has resulted in improved accessibility for veterinary use in the UK. This case series describes clinical outcomes of cats with FIP treated with injectable remdesivir and oral GS-441524. Twenty-five cats were diagnosed with FIP at a referral hospital in the UK between August 2021 and March 2022. Diagnosis was based on a combination of clinical signs, laboratory, imaging and cytological findings, and immunocytochemistry. Twenty cats presented with effusive FIP and 5 cats with non-effusive FIP. Five cats had neurological signs and 4 cats had significant ocular involvement. At the time of writing, 10 cats had successfully completed an 84-day course of remdesivir and GS-441524 treatment with complete clinical and biochemical remission. Ten cats were in clinical remission and still receiving treatment and 5 cats were euthanised a median of 2 days (range 1-13) after starting treatment. All surviving cats received remdesivir intravenously for a median of 5 days (range 2-9) at a median dose of 15 mg/kg (range 10-20). Higher doses were used for cats with non-effusive FIP, neurological or ocular signs, and for effusive cases presenting with severe clinical signs. All 20 cats demonstrated significant clinical response after a median of 2 days (range 2-5). Two cats received subcutaneous remdesivir treatment only following initial intravenous therapy. Eight cats received subcutaneous remdesivir for a median of 14 days (range 4-68) before transitioning onto an equivalent dose of oral GS- 441524. Ten cats received oral GS-441524 treatment immediately following intravenous remdesivir therapy. Both drugs were well tolerated although local skin reactions and pain with subcutaneous injections of remdesivir was observed. Of the five cats that were euthanised, three cats were euthanised within 3 days of starting treatment as a result of comorbidities or financial constraints. One ragdoll developed a T3-L3 myelopathy 7 days into treatment with 15mg/kg remdesivir, with no clinical improvement following dose escalation. Post-mortem confirmed FIP within the central nervous system. Another ragdoll also developed central nervous system signs 13 days into treatment with 20mg/kg remdesivir and was subsequently euthanised. This case series demonstrated the successful use of injectable remdesivir and oral GS-441524 for the treatment of FIP in 20 out of 25 (80%) cats.