Feline infectious peritonitis (FIP) was previously a uniformly fatal disease in cats. The development of antiviral treatments based on GS-441524 and related nucleoside analogues has transformed FIP from a death sentence to a treatable condition — with significant welfare implications.
Untreated FIP causes severe suffering: wet FIP causes massive effusion compressing lungs and abdominal organs; dry FIP causes progressive weight loss, fever, and organ failure. Before antiviral availability, euthanasia was typically recommended within weeks of diagnosis to prevent prolonged suffering. GS-441524 treatment causes rapid clinical improvement within 1-7 days in most cats, transforming the welfare experience dramatically. However, treatment inequality — determined entirely by owner finances — means many cats still die of a now-treatable disease. Relapse, requiring extended or second-line treatment, occurs in approximately 15% of cases. Monitoring during treatment includes regular blood work and clinical assessment.