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Tawny before after

Photos by Wendy Novicoff

Tawny was diagnosed in 2020 at age four months with a form of feline infectious peritonitis that affected her eyes (top). Her owner, Wendy Novicoff, quickly began treating her with an imported compound she obtained through contacts on Facebook. It was likely a version of GS-441524, an antiviral known to reverse the disease. After 12 weeks of treatment with the black-market product, Tawny showed no signs of illness (bottom). Novicoff, a professor of orthopedic surgery and public health sciences at the University of Virginia School of Medicine, has become an advocate for legal FIP drugs.

A veterinary compounding pharmacy in New Jersey has announced it will make available an oral treatment for feline infectious peritonitis starting in June. The tablets for individual patients with a prescription will be the first veterinary FIP treatment sold in the United States.

"It's a big, transformative day for us in the world of FIP therapy," said Dr. Samantha Evans. An assistant professor of clinical pathology at Colorado State University College of Veterinary Medicine and Biomedical Sciences, Evans has been researching treatments for FIP since 2020.

FIP is a rare and devastating response in cats to infection by a common pathogen, feline enteric coronavirus (FECV). Most cats infected with FECV are asymptomatic and remain healthy. But occasionally, the virus mutates in such a way that it infects immune system cells, which disseminate and cause inflammation that is deadly without treatment.

The road to an effective treatment has been long and frustrating. In the late 2010s, researchers at the University of California, Davis, School of Veterinary Medicine discovered that an antiviral agent called GS-441524 reversed FIP. However, the patent holder, Gilead Sciences, never applied to the U.S. Food and Drug Administration for approval to sell it.

Cat owners have obtained black-market versions of GS-441524, in injectable and pill forms, to treat sick pets on their own. The unauthorized treatments have been found to be effective. A survey of owners by Evans and colleagues, results of which were published in 2021, found survival rates of 80% and better for cats using the black market treatments.

A related antiviral medication, remdesivir, has also been found to work well against FIP. An injectable form of the drug was approved by the FDA in 2020 to treat Covid-19 in humans. Remdesivir may be prescribed for off-label veterinary use, but supplies are so limited that many cat owners continue to use black market GS-441524.

In 2021, Bova, a veterinary pharmaceutical company based in the United Kingdom and Australia, began compounding GS-441524 for veterinarians. It now provides the medication in parts of Europe, Australia, Canada and other countries.

In the U.S., compounder Stokes Pharmacy says in its website announcement that it has formed a relationship with Bova to offer that same medication for domestic sale.

A co-owner at Stokes Pharmacy designated to talk about the FIP treatment was unavailable this week. Bova referred all questions to Stokes.

A legal gray area

Because GS-441524 is not available as an FDA-approved drug, Stokes presumably will compound it from bulk active pharmaceutical ingredients, a practice that falls into a complicated gray area in terms of the law.

Technically, veterinary compounding using bulk ingredients is illegal in the U.S. However, understanding that veterinary compounding using bulk ingredients is sometimes medically appropriate, the FDA has produced guidelines that outline the circumstances under which it will exercise what it calls "enforcement discretion."

The guidelines state, for example, that the FDA "generally does not intend to take enforcement action" when there is not an FDA-approved product with the same active ingredient.

Asked about Stokes' announcement, FDA spokesperson Siobhan DeLancey said, "The FDA is aware of Stokes Pharmacy's announcement that it will begin marketing a compounded version of GS-441524 and is still obtaining additional information."

FIP researcher Evans, who is not affiliated with either Stokes or Bova, anticipates speed bumps in the rollout of the medication.

"There's possibly going to be some issues with supply, because we know there's going to be huge demand at the outset," she said. "People will have to be patient a little bit with that." FIP is estimated to affect around 1.3% of cats, most often kittens in catteries and shelters.

In addition, the tablet form won't work for every case. While oral drugs are great for patients that can eat, Evans said, "they're not so great for animals that are tanking and crashing on the table."

She added: "I'm trying to be realistic about this, but it's still very exciting."

May 10 update: The FDA announced that it "does not intend to enforce new animal drug approval requirements for products compounded from GS-441524, when prescribed by a veterinarian for a specific cat patient" to treat FIP. In other words, the regulator will allow the sale and use of the compounded treatment.