# Efficacy of GS-441524 for Feline Infectious Peritonitistis: A Systematic Review (2018-2024)
## 4 Discussion
There is no common regulatory standard between countries, which makes it difficult even for clinicians in the field to understand what treatment options are legally available in their country. For this reason, veterinarians might not even consider GS-441524 or its analogues as a treatment option for FIP. Limitations: The main limitations of this review stem from the available studies. All data were from uncontrolled trials; hence, improvements in cats could theoretically have been influenced by ancillary care or spontaneous recovery (though spontaneous recovery from FIP is exceedingly rare). Controlled randomized studies are needed to confirm the efficacy of GS-441524 in the treatment of FIP to increase the certainty level of any conclusion on the matter and to draw clear and practical guidelines on the use of the antiviral in FIP patients. Currently, the data available is not statistically robust enough to allow veterinarians to implement rules and guidance in clinical decision-making. For instance, no statistically based conclusion can be drawn on whether neurological FIP should be treated with combination therapy or a monotherapy, or which dosage should be used and for how long. The conclusions on this matter are based on experience and not evidence, due to the absence of controlled randomized studies. Publication bias is likely-- veterinarians or owners who had great success might be more inclined to publish than those with failures. However, given the consistent reports from various independent groups, the efficacy signal is strong. We also had to rely on pooled data that combine different dosing regimens and case mixes. There is inherent heterogeneity: for example, one study might focus on CNS cases on high doses, while another was mostly uncomplicated cases on standard doses--comparing results between them is not straightforward. Wherever possible, we stratified data to make \"apples to apples\" comparisons. Another limitation important to highlight is that the age of the fellines we analyzed was not always available. We were therefore unable to include this parameter as part of our study. We acknowledge this may be a significant factor in the response to treatment. The literature does not yet contain multiple and consistent examples of age being a significant factor affecting GS-441524 efficacy when treating effusive vs. non-effusive FIP. In one of the studies we analyzed [11], a field trial involving 31 cats, with ages 3.4 to 73 months (approx. 0.3-6 years), had 26 effusive and 5 non-effusive cases. Older cats and non-effusive cats responded as well as young cats and those with effusive FIP. But this is just one example, and clearly more studies are needed to assess this issue adequately. Five of the eleven included studies used gold standard methodologies, with a further five using a thorough range of techniques, including PCR. Only one study [9] lacked adequate details, with cats presumed to have FIP based on prior veterinary diagnosis, but no details are provided. As a further limitation of our review, it may be possible that some of these cases were not actually FIP, though as a cohort of just 26 cases, and for each, the outcome defined as \"relapse and change treatment\", they did not impact upon the data we calculated for remission or death. Future Directions: What the field needs now are controlled randomized clinical trials. A randomized trial of GS-441524 (or its prodrug) at different doses would help determine the minimum effective dose and confirm that the outcomes are truly as good as they appear. Trials comparing GS-441524 monotherapy vs. combination (e.g., with an adjunct like GC376 or Molnupiravir) would be valuable, particularly for neurologic FIP. Additionally, long-term follow-up of treated cats is needed to ensure there are no late relapses or chronic issues. Thus far, reports of cats cured of FIP show they live normal lives and even successfully receive vaccinations or deal with other illnesses without FIP recurrence [11].