Table of Contents
Last reviewed: 2026-07
FIP (Feline Infectious Peritonitis) Triage
Feline Infectious Peritonitis (FIP) was historically considered a 100% fatal diagnosis. Today, with the availability of antiviral treatments like GS-441524, FIP is highly treatable. However, because FIP progresses rapidly, immediate triage and starting treatment early is critical to your cat's survival.
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- Abdominal swelling (fluid buildup)
- Persistent high fever unresponsive to antibiotics
- Severe lethargy and weakness
- Yellowing of the eyes or skin (jaundice)
- Neurological symptoms like stumbling or seizures
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Safe to Monitor at Home
- Isolated mild lethargy without fever
- Eating normally despite slight weight loss
In our experience
In our experience, a cat that won't lift its head for its favorite treat is a cat that needs a vet immediately. Never ignore profound lethargy.
What an FIP Diagnosis Looks Like Today
FIP comes in two broad forms: effusive ("wet"), with fluid building up in the belly or chest, and non-effusive ("dry"), which often shows as fever, weight loss, eye changes, or neurological signs. Vets typically combine bloodwork (a low albumin-to-globulin ratio is a common flag), fluid analysis when effusion is present, and imaging. Diagnosis can take a few days — push for urgency, because treatment works best when started early.
The Treatment Reality
Antiviral treatment with GS-441524 has transformed FIP from a death sentence into a condition with high survival rates, and it is now legally available through veterinarians in a growing number of countries, including via compounding pharmacies in the United States. A standard course runs about 12 weeks, followed by an observation period to watch for relapse. It is a real commitment — daily medication and periodic bloodwork — but the cats that complete it usually return to fully normal lives. If your vet is not experienced with FIP treatment, ask for a referral; experience with dosing protocols and relapse monitoring matters.