FIP Treatment FAQ

What is the Efficacy of GS-441524 for Treating FIP?

While FIP was once a 100% deadly disease, GS-441524 effectively stops FIP virus replication and successfully treats this once fatal disease (Murphy at al., 2018). Moreover, Pedersen (2019) writes that GS-441524 has proven to be a highly effective and safe treatment for feline infectious peritonitis. 

In one study of 307 cats treated with remdesivir and GS-441524 for instance, the success rate was found to be 84.4%. When administered at the recommended dosages and treatment duration, GS-441524 has demonstrated high efficacy in treating all forms of FIP (Taylor et al., 2022). Various other studies have shown success rates ranging from 81% – 96.7% (Jones et al., 2021; Coggins et al., 2023; Green et al., 2023).

Can Steroids be used with FIP treatment? 

In certain cases, short-term steroid administration is necessary to reduce inflammation and stabilize FIP patients, particularly those with severe neurological symptoms. For cats with IMHA or other secondary conditions requiring steroid therapy, longer term use may be required. As steroids have an immune suppressing effect, their use should be minimized whenever possible. For cats with ocular FIP, topical steroids are often prescribed to manage uveitis. When FIP patients require anti-inflammatory treatment, NSAIDs can be considered as an alternative where appropriate (Taylor et al., 2025).

Should GS-441524 be Used to Eliminate Feline Enteric Coronavirus (FECV)?

Pedersen (2020) strongly advises against treating healthy cats with GS to eradicate FECV. This approach is ineffective in preventing reinfection with the coronavirus and future development of FIP. Moreover, preventative treatment can lead to GS drug resistance and the reduced or complete lack of efficacy of GS if the cat develops FIP in the future. The rise of resistant FIP cases requiring alternative antivirals is already a concern. Unnecessary preventative treatment will only exacerbate this issue and clearly contradicts responsible antimicrobial stewardship principles (Pedersen, 2020).

What are the Vaccination Recommendations During and After FIP Treatment?

While specific data is limited, available evidence suggests that cats can be vaccinated during treatment if necessary or after successful FIP treatment without a relapse. Vaccination decisions should follow guidelines (see WSAVA) based on the cat’s environment and risk. If urgent vaccination is necessary during treatment due to high disease risk, it is best to wait until the cat is clinically stable (Taylor et al., 2025).

Can Parasite Control be used With FIP Treatment?

Routine deworming and flea treatment are safe during GS-441524 treatment.

When Should FIP Cats be Spayed and Neutered?

If the cat responds well to treatment, the spay or neuter procedure can be performed a month after ending treatment. However, for many cats, an unaltered state can cause stress, and in those cases, spay/neuter can be done during the treatment providing that the cat is stable and there are 2-4 weeks of treatment remaining (Taylor et al., 2025).

What is the Difference Between Pharmacy Compounded GS-441524 & Unregulated/Black Market GS?

Pharmacies in Canada are required to source their raw GS-441524 from Health Canada registered, GMP compliant wholesalers, ensuring quality control. Veterinarians can inquire directly about a pharmacy’s quality standards (Guidance on drug establishment licences, 2024).

In contrast, there are no guarantees with the black market forms of GS. While they have saved thousands of lives when there was no licenced alternative, as Kent et al. (2024) have shown, there can be a wide variance in what unregulated GS is advertised as vs. what it contains. Black market oral GS was found in many cases to be drastically under-concentrated. 

References:

Coggins, S. J., Norris, J. M., Malik, R., Govendir, M., Hall, E. J., Kimble, B., & Thompson, M. F. (2023). Outcomes of treatment of cats with feline infectious peritonitis using parenterally administered remdesivir, with or without transition to orally administered GS-441524. Journal of veterinary internal medicine, 37(5), 1772–1783. https://doi.org/10.1111/jvim.16803

Green, J., Syme, H., & Tayler, S. (2023). Thirty-two cats with effusive or non-effusive feline infectious peritonitis treated with a combination of remdesivir and GS-441524. Journal of veterinary internal medicine, 37(5), 1784–1793. https://doi.org/10.1111/jvim.16804

Guidance on drug establishment licences (GUI-0002) (2024). Government of Canada Web site: https://canada.ca/en/health-canada/services/drugs-health-products/compliance-enforcement/establishment-licences/directives-guidance-documents-policies/guidance-drug-establishment-licences-drug-establishment-licensing-fees-0002/document.html

Jones, S., Novicoff, W., Nadeau, J., & Evans, S. (2021). Unlicensed GS-441524-Like Antiviral Therapy Can Be Effective for at-Home Treatment of Feline Infectious Peritonitis. Animals, 11(8), 2257. https://doi.org/10.3390/ani11082257

Pedersen, N. C., Perron, M., Bannasch, M., Montgomery, E., Murakami, E., Liepnieks, M., & Liu, H. (2019). Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. Journal of feline medicine and surgery, 21(4), 271–281. https://doi.org/10.1177/1098612X19825701

Pedersen, N. C. (2020). The inappropriate use of GS. www.sockfip.org/inappropriate-use-of-gs-441524-in-an-attempt-to-eliminate-feline-enteric-coronavirus-fecv-from-healthy-cats/

Kent, A. M., Guan, S., Jacque, N., Novicoff, W., & Evans, S. J. M. (2024). Unlicensed antiviral products used for the at-home treatment of feline infectious peritonitis contain GS-441524 at significantly different amounts than advertised. Journal of the American Veterinary Medical Association, 262(4), 489–497. https://doi.org/10.2460/javma.23.08.0466

Taylor, S., Tasker, S., Barker, E. & Gunn-Moore, D., Sorrell, S., Cerna, P. & Coggins, S. (2025). icatcare_fipupdate_July25. https://icatcare.org/resources/icatcare_fipupdate_july25.pdf