Demystifying FIP: Testing, treatment advances, and practical takeaways

In recent years, there are been notable strides for treating feline infectious peritonitis (FIP), especially in 2024 with GS-441524 becoming available in the US and Wedgewood becoming the first US veterinary compounding pharmacy to offer molnupiravir.^1,2

On this week's episode of The Vet Blast Podcast presented by dvm360, our host Adam Christman, DVM, MBA, and guest Kelly Chappell, DVM, DACVIM (Small Animal) talk more about the current state of treating FIP in veterinary medicine, with deeper dives into the struggles to definitively diagnose it in clinical practice as well as treatment and alternatives available, and more.

Below is a partial transcript, edited lightly for clarity

Adam Christman, DVM, MBA: All right, so FIP, since we can very rarely obtain a definitive diagnosis of it in clinical practice, what testing and tools can we use for a more presumptive FIP diagnosis?

Kelly Chappell, DVM, DACVIM (Small Animal): I's such a good question, and I will say the diagnosis of FIP is still the bane of my existence. As happy as I am that we can treat it, diagnosis is still super frustrating. As most people know, definitive diagnosis is really going to be with that histopathology and immunohistochemistry, which requires us to get surgical samples, which require surgery and anesthesia, which most of the time we're not going to put these sick cats through. So a lot of time we are relying on a more presumptive diagnosis.

I often think about it as a building block system, as I'm often trying to check a certain number of boxes to make myself feel like I'm fitting into that presumptive diagnosis. One of the first building blocks that I'll look at is really the signalment and the vitals. FIP can really occur in any age cat, but we definitely see it in cats less than 2 year olds, most commonly pure breed cats, and male cats are also slightly over represented in some studies.

Fever is really common in cats with FIP, with about 70% of cats with FIP having a fever. In a 2017 study that looked at cats with fevers, FIP was the most common condition diagnosed in cats referred for fever. So whenever I see a young cat with a fever, it always like picks my little FIP flags up.

One of the next building blocks I'll really commonly look at is a chemistry panel really looking at the globulins, albumin to globulin ratio, and bilirubin. The globulin number itself could still be a normal range, but could still have an abnormal albumin [to] globulin ratio. So if my [chemistry] panel doesn't automatically calculate my albumin [to] globulin ratio, I'm always just calculating that. Cat and albumin-globulin ratio greater than 0.8 has a really high negative predictive value, meaning it's really helpful in ruling out FIP. So if I have a cat where maybe I have FIP on my differential list and it's greater than 0.8 I feel pretty good to bring it lower down on my differential list. And albumin [to] globulin ratio, less than 0.6 and especially less than 0.4 again, is another thing that peaks my flags up for FIP in those cats.

References

1. McCafferty C. Compounded oral FIP treatment is now available. dvm360. Published June 14, 2024. Accessed November 18, 2025. https://www.dvm360.com/view/compounded-oral-fip-treatment-is-now-available
2. McCafferty C. Wedgewood announces FIP treatment. dvm360. Published September 19, 2024. Accessed November 18, 2025. https://www.dvm360.com/view/wedgewood-announces-fip-treatment