GS-441524 in the Treatment of Feline Infectious Peritonitis: When to Choose Oral or Injectable Forms
Feline infectious peritonitis (FIP) is a devastating disease that was once 100% fatal. However, thanks to significant progress in research trials over the past several years, GS-441524 has been shown to be a highly effective and safe antiviral treatment, with success rates ranging from 84.4% to 96.8% in multiple studies (Taylor et al., 2022, Coggins et al., 2023; Green et al., 2023).
The Evolution of Treatment Protocols
Since 2020, veterinarians in Australia and the UK have had access to regulated GS-441524 and Remdesivir (Taylor et al., 2025). While GS was originally developed as an injectable drug, the shift to oral administration proved to be a significant advancement, transforming a treatment that was once limited mainly to injections, into a more practical option for cat owners (FIP treatment GS-441524 – now available in the U.S., n.d.).
In one study of 307 cats, conducted from 2020-2022, both oral GS-441524 and Remdesivir were shown to be highly effective in treating FIP. The authors concluded that the ease of administering oral GS tablets compared to injectable Remdesivir, which caused pain upon administration, was likely to make the oral form the preferred front-line treatment option in countries where it is legally available. They determined that injectable Remdesivir was still appropriate to be used in situations where it was the only form of treatment legally available or in the rare cases where cats could not initially tolerate oral medication (Taylor et al., 2022).
While initially the protocol was to start cats with Remdesivir injections and then transition to oral GS, research has since confirmed that oral GS-441524 can be used successfully from day one of treatment in nearly all cases. This has several advantages, including:
– Effective from the start: Oral GS-441524 has proven to be just as effective as injectable forms when given from the beginning.
– Pain-free treatment: Oral GS eliminates the pain associated with injections.
– Reduced risk: Eliminates the risk of injection site sarcomas.
– Versatile treatment: Cats with all forms of FIP can be treated with oral GS-441524 (Taylor et al., 2025).
When is Injectable Treatment Indicated?
According to International Cat Care guidelines, injectable treatment should be reserved for specific cases, such as:
* Cats that are severely dehydrated and ill.
* Cats with severe neurological symptoms, such as those that cannot swallow or take oral medication, will benefit from injectable treatment.
*Cats that cannot take oral medication safely due to other reasons may require injectable treatment (Taylor et al., 2025).
A New Era of Quality-Controlled Treatment:
For several years in North America, the unregulated form of GS-441524 was the only drug accessible for cat owners. As of February 2024 in Canada and June 2024 in the US, veterinarians have had access to regulated GS-441524 for patient prescriptions, eliminating the need for cat owners to rely on unregulated or black market channels. Oral GS-441524 is available from multiple pharmacies in multiple modalities, such as oral suspension, tablets and capsules. The injectable form of GS is also available through certain pharmacies in both the US and Canada.
As noted by Weese (2025), with access to compounded GS-441524 from licensed pharmacies, quality control is no longer a concern, ensuring that cats receive the effective treatment they need.
The advent of oral GS-441524 has revolutionized FIP treatment, offering a safe, effective, and pain-free option for cats. This makes the treatment process both easier for the patient and for the caregivers.
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.
FIP treatment GS-441524 – now available in the U.S. (n.d.). Cornell University, College of Veterinary Medicine Web site: https://www.vet.cornell.edu/
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.
Taylor, S. S., Coggins, S., Barker, E. N. & Gunn-moore, D., Jeevaratnam. K., Norris, J. M., Hughes, D., Stacey, E., Macfarlane, L., O’brien, C., Korman, R., Mclauchlan. G., Torres, X. S., Taylor, A., Bongers, J., Espada Castro, L., Foreman, M., Mcmurrough, J., Thomas, B., Royaux, E., Calvo Saiz, I., Bertoldi, G., Harlos, C., … Tasker, S. (2020–2022). Retrospective study and outcome of 307 cats with feline infectious peritonitis treated with legally sourced veterinary compounded preparations of remdesivir and GS-441524. Journal of Feline Medicine and Surgery, 92023;25. https://doi.org/10.1177/
Taylor, S., Tasker, S., Barker, E. & Gunn-Moore, D., Sorrell, S., Cerna, P. & Coggins, S.
(2025). Icatcare_fipupdate_July25. Click to access icatcare_fip_update_july25.pdf
Weese, S. (2024, November 20). Update: FIP drug access in Canada. https://www.wormsandgermsblog.
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