Treatment for Feline Infectious Peritonitis

Laurie Anne Walden, DVM

Photo by Borna Bevanda on Unsplash

Feline infectious peritonitis (FIP) is a viral disease that until recently was untreatable and almost always fatal in cats. An effective antiviral drug emerged a few years ago but was legally unavailable in the United States. Some cat owners bought the drug at high cost on the international black market, but this product was unregulated, untested, and possibly unsafe.
 
A compounded version of this antiviral drug, GS-441524, is now available in the United States by veterinary prescription. This means that FIP has become a treatable disease instead of a near-certain death warrant for cats.
 
The US Food and Drug Administration (FDA) hasn’t officially approved the compounded product for use in cats. However, the FDA announced that because no approved drug is available, it won’t enforce drug approval requirements when a veterinarian prescribes this product for an individual cat.[1]
 
Signs and Diagnosis of FIP
The virus that causes FIP is a coronavirus. Feline coronavirus infection is very common in cats. The virus typically lives in the intestines without causing much trouble. In some cats, feline coronavirus mutates into a disease-causing strain that spreads through the body. This disease is FIP.
 
The signs of FIP depend on whether a cat has the “wet” form (with fluid accumulation in the chest and abdomen) or the “dry” form (with inflammatory masses and other changes in the eyes, nervous system, kidneys, liver, or other organs). Some of the signs are swollen belly, decreased appetite, decreased energy, weight loss, fever, labored breathing, blindness, and seizures.
 
Because the signs of FIP are nonspecific and because so many cats have been infected with feline coronavirus, diagnosis is not simple. The diagnosis is often presumptive, meaning that it’s not confirmed by definite tests but is suspected on the basis of clinical signs and the results of blood and urine tests, imaging studies, fluid analysis, and biopsy.
 
Treatment
GS-441524 is a metabolite of remdesivir. Remdesivir is used to treat COVID-19 in humans, but it’s not licensed for use in animals. Veterinarians can treat animals off label with drugs licensed for humans, so remdesivir is technically a treatment option for cats but it’s hard for veterinarians to access.
 
Unlike remdesivir (an injectable product), compounded GS-441524 is a tuna-flavored tablet. It’s already being used to treat cats in Australia and the United Kingdom. The dose depends on the cat’s clinical signs, and the current recommendation is to continue treatment for 12 weeks.
 
Reported survival rates for cats treated with GS-441524 range from 81% to 100%.[2] Without this treatment—or a similar antiviral drug if one becomes available—the prognosis is grim.
 
References
1. FDA announces position on use of compounded GS-441524 to treat FIP. US Food and Drug Administration. May 10, 2024. Accessed September 3, 2024. https://www.fda.gov/animal-veterinary/cvm-updates/fda-announces-position-use-compounded-gs-441524-treat-fip
2. Tasker S, Addie DD, Egberink H, et al. Feline infectious peritonitis: European Advisory Board on Cat Diseases guidelines. Viruses. 2023;15(9):1847. doi:10.3390/v15091847
 
Image source: https://unsplash.com/photos/gray-tabby-kitten-leaning-on-white-wall-VwqecUsYKvs

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