# Efficacy of GS-441524 for Feline Infectious Peritonitistis: A Systematic Review (2018-2024)
## 3 Results
### GS-441524 Monotherapy vs. Combination Therapy  
Eight of the eleven studies (covering 551 of the 650 cats) evaluated GS-441524 as a stand-alone treatment (with only supportive care). In that combined cohort, the success rate was 83.1% (458/551) for GS-441524 monotherapy. The remaining cases in our dataset involved GS-441524 used in combination with other treatments:  
* GS-441524 + Interferon omega: One study (12 cats total) reported using feline interferon-\(\omega\) alongside GS-441524 in primarily dry FIP cases. Notably, all 12 cats survived (1 required an extra GS-441524 cycle) for an effective success rate of \(\sim\)100% in that small sample. This regimen was associated with prolonged interferon therapy (up to 1 year) following a standard GS-441524 course [21]. Due to the small number of fellines in these studies, no failure was reported in this treatment group, which means that the effectiveness of the treatment can not be assessed statistically.
* GS-441524 + Remdesivir: Two studies (37 cats) combined GS-441524 (oral) with injectable Remdesivir [8,22]. Remdesivir was either given initially for a few days or concurrently. Outcome: 35/37 survived (94.6% success). Statistically, this was not different from GS-441524 alone (\(p\) = 0.066) and we can not exclude that the better outcome in this drug's combination is not due to chance. All cats with neurological signs in this group survived, but numbers were too small to obtain a small \(p\)-value and draw firm statistical conclusions.
* GS-441524 + GC376: Two studies (48 cats) combined GS-441524 with GC376 [9,23]. Outcome: 45/48 survived (93.8% success). Again, not statistically superior to monotherapy (\(p\) = 0.054). Among those with non-effusive FIP and concurrent GC376, success was 94% (including two relapses that were retreated successfully). The addition of GC376 did not clearly overcome the challenge of neurologic disease (one cat with CNS signs relapsed).  
Pooling all combination-therapy cases (n = 97) yields a success rate of \(\sim\)94.8%, compared to 83.1% for monotherapy. This numeric difference identifies a possible advantage to combination therapy in tough cases, but the OR and RR confidence intervals for combination vs. monotherapy crossed one (OR \(\sim\)2.3 [0.8-6.7]; RR \(\sim\)1.14 [0.98-1.33]; \(p\) = 0.11). This means that the improved outcome following combination therapy can be due to chance, and a poorer outcome is also statistically possible and plausible. For instance, it is statistically possible to obtain the opposite outcome with another case series studying combination therapy on a different group of fellines with FIP. Thus, while combination regimens showed excellent outcomes, especially in small cohorts, we cannot conclusively say they are superior to GS-441524 alone given the current data. It is worth noting that no failures were reported in the interferon combination group (hence an incalculable OR for that subgroup), pointing to potential synergy that warrants further investigation (Table 5). The effectiveness of treatment is not called in question, but the superiority of one treatment over another needs further research to be assessed and draw statistically significant conclusions.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Comparison—Efficacy of** & & & & \\
**Treatment in** & & & & \\
**Effusive FIP vs.** & & & & \\ \hline GS-441524 Monotherapy in & & & & \\ Mixed FIP & & & & \\ \hline GS-441524 Monotherapy in & & & & \\ Non-effusive FIP & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Odds ratio, relative risk, and risk difference for the efficacy of treatment in wet FIP compared to mixed and dry FIP, with a 95% confidence interval.