Harmony Vet Team, DVM PhD Oct 1, 2024

Introduction

Feline Infectious Peritonitis (FIP) was first described in 1963 (1) and was considered fatal to cats until 2019 when Dr. Pedersen and his team at the University of California, Davis, published the first successful treatment using GS-441524, a molecule with antiviral properties (2). This initial treatment involved administering injections over 84 days. However, the injectable form of GS-441524 is stable only in a very acidic solution (pH 1.5 - 2), making the injections painful and causing skin sores and fibrosis over time. Consequently, suppliers developed oral formulations, such as tablets and capsules, to alleviate these issues.

Concerns and Comparative Efficacy

Oral administration of medications often raises concerns about efficiency compared to injections due to the involvement of the gastrointestinal tract, which can affect drug absorption. In both human and veterinary medicine, oral dosages are typically adjusted to account for partial absorption. For instance, the anti-nausea medication Cerenia is administered at 1 mg/kg when injected but requires 2 mg/kg when given orally.

The efficacy of oral GS-441524 was first demonstrated when cats transitioned from a month of injections to an adjusted oral dosage. The first scientific article documenting successful treatment using only oral tablets was published in 2021 (3). Since then, thousands of cats have been successfully treated and cured with oral GS-441524, with multiple studies confirming these results (4, 5, 6). Cats diagnosed with FIP can now start treatment with oral forms (tablets or capsules) and achieve the same success rates as those treated with injections.

Advantages of Oral Treatment

Oral treatment is often preferred over injections due to ease of administration, which ensures compliance and adherence to the treatment regimen. Proper adherence is crucial for the success of FIP treatment. Currently, a cat treated at the appropriate dose with the necessary supportive care has an above 85% chance of being cured.

Exceptions to Oral Treatment

In less than 5% of cases, oral treatment may not be suitable for all cats. Exceptions include:

1. Cats in critical condition requiring hospitalization and unable to swallow.

2. Cats that consistently vomit or have uncontrollable diarrhea.

3. Rare cases where cats do not absorb the oral form correctly. This should be considered if a cat does not respond to treatment despite dosage adjustments.

However, most cats can transition from injections to oral treatment after one to four weeks of initial therapy, provided the exceptions listed above improve with the injections.

Conclusion

More than 95% of cats respond well to only oral GS-441524 treatment for FIP (starting on oral treatment from day 1), provided the treatment regimen is rigorously followed. Oral treatment is as efficient as injections for Feline Infectious Peritonitis, offering a less painful and more manageable alternative for cat owners and veterinarians.

References

1. Pedersen, N. C. (2009). A review of feline infectious peritonitis virus infection: 1963–2008. Journal of Feline Medicine and Surgery, 11(4), 225-258.

2. 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.

3. Krentz, D., Zenger, K., Alberer, M., Felten, S., Bergmann, M., Dorsch, R., ... & Hartmann, K. (2021). Curing cats with feline infectious peritonitis with an oral multi-component drug containing GS-441524. Viruses, 13(11), 2228.

4. Zwicklbauer, K., Krentz, D., Bergmann, M., Felten, S., Dorsch, R., Fischer, A., ... & Hartmann, K. (2023). Long-term follow-up of cats in complete remission after treatment of feline infectious peritonitis with oral GS-441524.Journal of Feline Medicine and Surgery, 25(8), 1098612X231183250.

5. Katayama, M., & Uemura, Y. (2023). Prognostic prediction for therapeutic effects of Mutian on 324 client-owned cats with feline infectious peritonitis based on clinical laboratory indicators and physical signs. Veterinary Sciences, 10(2), 136.

6. Cosaro, E., Pires, J., Castillo, D., Murphy, B. G., & Reagan, K. L. (2023). Efficacy of oral remdesivir compared to GS-441524 for treatment of cats with naturally occurring effusive feline infectious peritonitis: a blinded, non- inferiority study. Viruses, 15(8), 1680.