Status of FIP Treatment in 2022

Niels C. Pedersen, DVM PhD
November 28, 2022

I am pleased to inform you that I have left my advisory role with SOCKFIP and now officially joined the SOCKFIP board. This reflects my transition from university to private life but will not affect my dedication to FIP research. Hopefully, this more direct involvement will be helpful in helping SOCKFIP transition for a broader role in issues concerning issues of feline health in addition to FIP. Research on FIP continues at UC Davis as well as other institutions worldwide. Research projects concerning FIP at UC Davis are summarized in the 2022 SOCK FIP Season’s Greetings. SOCKFIP, through public donations, continues to provide financial assistance for such studies and I provide scientific input whenever needed.

I wish that licensed antiviral treatments for FIP in cats would exist, but efforts by many individuals and groups have failed to alter the current reality. Therefore, it is doubtful that legal anti-viral drugs for FIP will be marketed in the next 2-5 years, even if the impediments were immediately removed. Fortunately, world-wide limitations on the general use of closely related human drugs for COVID-19 are being loosened, allowing them to be prescribed by all physicians and employed more broadly in the field. Full approval for humans allows for their use in animals, provided that the needed drug is derived directly from the actual human product. This would make it legal to use human manufactured drugssuch as Remdesivir and Molnupiravir (EIDD-2801) in animals,although at the human price. The goal should still be drugs specifically licensed for animals and available at a veterinary and not medical price.

More and more veterinarians now assisting owners in the treatment. I remain disappointed, however, that some veterinarians have not heard about effective treatments for FIP, believe that published reports on the treatment were bogus, or that sourcing drugs from unapproved markets is so egregious that they cannot even assist with the treatment once purchased by an owner. I commend those veterinarians that accept the reality of the treatment and work with owners and their cats with FIP.

The most significant discovery since GS-441524 is the use of Molnupiravir (EIDD-2801) (Merck) as a second effective treatment for FIP. Molnupiravir has also particularly effective in the treatment of cats that have developed resistance to GS-441524, which is most commonly cats that have developed neurological FIP during or after GS-441524 treatment.

I believe that several areas of research warrant consideration by veterinary researchers. One area concernsthe safety and efficacy of EIDD-1931 (Beta-d-N4-hydroxycytidine), which is the biologically active moiety of Molnupiravir, just as GS-441524 is the active component of Remdesivir. This orally given drug has been researched for almost a half century and should be no longer patent protected. Preliminary research at UC Davis suggests that it may be even more effective and saferthan Molnupiravir. I also believe that the orally administered protease inhibitor component (nirmatrelvir) of Paxlovid (Pfizer) should be tested against nonocular/neurological cases of FIP. Nirmatrelvir is broken down to a simple chemical modification of GC373, the active form of GC376. Paxlovid is widely available and can be readily prescribed by both pharmacists and physicians for general treatment of COVID-19. This should make it widely available for use by veterinarians. I also believe that much more research should be done on finding ways to limit FECV infection and to understand the factors that inhibit the natural normal protective immunity to FECV mutants as they occur. It is now apparent that most healthy cats have a strong natural and acquired immunity to FIP viruses. What is this immunity and how can this knowledge bolster FIP immunity?