FIP antiviral success brings a new stewardship challenge

Access to effective antivirals has changed the outlook for feline infectious peritonitis, but a new warning from infectious disease specialist Scott Weese argues the profession could undermine that progress if these drugs are used too loosely. In a March 2025 Worms & Germs post, Weese says the biggest resistance risk is not routine treatment of confirmed FIP cases, where cat-to-cat spread of FIP virus is thought to be rare, but broader use of GS-441524 against enteric feline coronavirus, which is common, transmissible, and shed in feces. That concern lands as FIP treatment keeps evolving: FDA said in May 2024 it does not intend to enforce approval requirements for veterinarian-prescribed, patient-specific compounded GS-441524 for FIP under specified conditions, even though the product remains unapproved, and newer guidance has pushed clinicians toward more tailored oral dosing and case-specific protocols. (wormsandgermsblog.com)

Why it matters: For veterinary teams, this is a stewardship story as much as a therapeutics story. The clinical upside of antivirals for true FIP is substantial, with studies and reviews showing strong outcomes for GS-441524, remdesivir, and, in selected settings, molnupiravir, but researchers are also now actively looking for resistance markers as use expands in the U.S. and elsewhere. The practical takeaway is to protect these drugs by tightening diagnosis, avoiding casual or population-level use for uncomplicated enteric coronavirus, and monitoring response closely when treatment is started. (vet.cornell.edu)

What to watch: Watch for emerging resistance surveillance data, especially from Cornell-led sequencing work, and for whether stewardship guidance becomes more formalized as legal access and off-label antiviral use continue to expand. (vet.cornell.edu)