Feline infectious peritonitis (FIP) in cats
FIP is caused by a mutated form of feline coronavirus. It was once almost always fatal, but antiviral treatment has changed that.
Last updated: October 2026 · 4 sources · see sources
Signs to watch for
- Fever that won't go away
- Swollen belly from fluid
- Weight loss
- Lethargy
- Eye or neurologic signs
Trouble breathing, collapse, repeated vomiting, not peeing, or a seizure that lasts more than a few minutes needs a vet right away. See when to see a vet.
How vets diagnose it
There's no single simple test. Vets combine bloodwork, fluid analysis, ultrasound and PCR. [3][4]
How it's treated
Antiviral drugs related to GS-441524 are now used, typically for about 12 weeks. [3][4]
What it costs to diagnose and manage
| Item | Typical US price | Src |
|---|---|---|
| Diagnosis (exam and tests) | $400–$1,000 | [1] |
| Compounded GS-441524, smallest listed pack (Stokes Pharmacy) | $195 | [2] |
These are typical US ranges from the sources listed. Your pet's costs depend on how severe things are, the tests your vet recommends, your pet's size and where you live. Ask your vet for a written estimate.
Outlook
Many cats now recover with antiviral treatment. [3][4]
Common questions
What is feline infectious peritonitis (FIP) in cats?
FIP is caused by a mutated form of feline coronavirus. It was once almost always fatal, but antiviral treatment has changed that.
What are the signs of feline infectious peritonitis (FIP)?
Common signs include: fever that won't go away, swollen belly from fluid, weight loss, lethargy, eye or neurologic signs.
How do vets diagnose feline infectious peritonitis (FIP)?
There's no single simple test. Vets combine bloodwork, fluid analysis, ultrasound and PCR.
How is feline infectious peritonitis (FIP) treated?
Antiviral drugs related to GS-441524 are now used, typically for about 12 weeks.
How much does feline infectious peritonitis (FIP) cost to treat?
Diagnosis (exam and tests): $400–$1,000; Compounded GS-441524, smallest listed pack (Stokes Pharmacy): $195. Costs vary with severity, tests, your pet's size and where you live.
Related
This page is general information for pet owners, not veterinary advice. Talk to your vet about your own pet.