Feline infectious peritonitis: From fatal to treatable

Abyssinian cats are more prone to develop FIP than other breeds. (Anobis/stock.adobe.com)Feline infectious peritonitis (FIP) has long carried a fatal designation, but according to top feline researchers and clinicians at the Winn Feline Foundation's recently held FIP symposium at the University of California-Davis (aptly titled “PURRsuing FIP and WINNing”), the disease should lose its lethal label.

Niels Pedersen, DVM, PhD, professor emeritus at the UC Davis School of Veterinary Medicine, opened a roundtable discussion on the topic of treatment options by explaining the two basic approaches to treating FIP: You can either stimulate the host's immune system to get rid of the virus, or you can attack the virus itself. The second category consists of both nonspecific and specific antivirals. Nonspecific antivirals include common drugs like itraconazole, an antifungal with antiviral properties.

The problem with these drugs, says Dr. Pedersen, is that you must deliver toxic amounts in order to get enough antiviral activity to inhibit the virus. In other words, you damage the host cat's cells along with the virus. Specific antivirals, on the other hand, hold more promise for the future of FIP treatment.

The lowdown on high hopes for specific antivirals

According to Dr. Pedersen, specific antivirals are small, easily absorbed molecules that target viral proteins without causing significant harm to the host's cells. Two of these specific antiviral compounds, GC376 and GS-441524, have shown efficacy in treating FIP, though neither drug has yet been granted FDA approval.

The rights for GC376, Dr. Pedersen briefly explained, were acquired by Anivive Lifesciences, which has begun the lengthy process of obtaining FDA approval for the treatment of cats with FIP. He noted that while he does think it's a promising drug, it's not without some problems (as evidenced by his 2018 research findings).

The future of GS-441524 is a bit more complicated. Dr. Pedersen explained that he was employed by Gilead Sciences around the time it was founded and that while working on the human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), he noticed that Gilead would make several iterations of the same drug compound. So after some promising experiences with GC376 and after hearing that Gilead was working on a drug for the potential treatment of Ebola (an RNA virus and a distant relative of the coronavirus), Dr. Pedersen reached out to Gilead to see if he could gain access to the drug and its iterations.

It took a year to sort out all of the details, but Dr. Pedersen eventually got the compounds, screened them, and landed on GS-441524. He and his colleagues performed pharmacokinetic studies and researched the compound's efficacy and safety against experimental FIP, finding it to be highly efficacious. They also published promising results from a field trial.

“And basically,” explained Dr. Pedersen, “all through this process we were led to believe that if there was something of importance to animals, there would be a chance to be granted animal rights-maybe not to us, but to somebody else.”

After the field trial, Dr. Pedersen put the ball in Gilead's court: “At that point we said, ‘Where's this going? We haven't had a firm agreement with you regarding animal rights.'”

Gilead came back with some disappointing news. “They let us know that we (or anyone else) wouldn't be granted animal rights for this compound because they'd discovered in the meantime that the compound was looking very promising for their Ebola research-the same compound in a somewhat different form,” Dr. Pedersen explained. “They were worried something would happen in the animal development side that would affect their ability to get the human form FDA approval. … Anything you find in any animal species has to be reported to the FDA, so if we were to find something bad in cats, it could completely poison the human side of it.”

Anything you can do, I can do on the black market

While he understood Gilead's stance, Dr. Pedersen did warn the company that if it continued to sit on GS-441524, someone else would take it and manufacture it for the black market. “And that's exactly what's happened,” he said. “Savvy people have been able to synthesize the compound themselves-all formulas have to be published, so this is all known.” The same has happened with GC376.

Dr. Pedersen noted that most of these savvy manufacturers are in Asia and that cat owner groups are acting as intermediaries between manufacturers and desperate pet owners. “I don't recommend people buy drugs from these sources, but I can't stop them either,” he explained. “It's an interesting situation to be in. The best I can do is encourage people to interact with their veterinarians-those veterinarians who will interact with them. … There are veterinarians who say they want nothing to do with this whole thing and that's fair enough. And there are veterinarians who say, ‘Listen. I will work with clients. If they can get the drugs, I will work with them to make sure the cat is properly monitored, that the drug is administered correctly and that the side effects are dealt with.'"

With GC376 and GS-441524, FIP's fatal days are numbered

Despite these obstacles, the overall mood in the room was optimistic. Brian Murphy, DVM, PhD, associate professor of microbiology and immunobiology at the UC Davis School of Veterinary Medicine, summed it up this way: “This is a treatable disease. We will cure this disease. We basically have the cure now. It's a matter of finding the exact right drug and combination and making it available at an affordable price.”

Sarah Mouton Dowdy, a former associate content specialist for dvm360.com, is a freelance writer and editor in Kansas City, Missouri.