Dickinson, Peter J., et al. "Antiviral treatment using the adenosine nucleoside analogue GS‐441524 in cats with clinically diagnosed neurological feline infectious peritonitis." Journal of Veterinary Internal Medicine (2020).
Summary: Dickinson et al. Treated 4 cats presenting with neurological FIP with the antiviral GS-441524. Evidence indicates that GS-441524 shows favorable clinical efficacy in treating cats with neurological FIP.
* Pedersen, Niels C., et al. "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 (2019): 271-281.
Summary: This is the main study showing strong clinical efficacy of GS-441524 acting as an effective treatment for cats with FIP. GS-441524 was effective at treating (likely curing) ~80% of cats enrolled in the study. For cats in treatment past the first week, 24 out of the 27 remaining cats (~90%) were healthy (likely cured) 9-months or longer after treatment.
Pedersen, Niels C., et al. "Efficacy of a 3C-like protease inhibitor in treating various forms of acquired feline infectious peritonitis." Journal of feline medicine and surgery 20.4 (2018): 378-392.
Summary: Study which details the use of the GC376 antiviral on treating FIP. This study was essential for establishing the 12-week treatment period. It also clearly details relapse symptoms and occurance, and documents the efficacy of increasing treatment concentrations to further suppress viral activity and symptoms. 7 out of 20 cats (~35%) showed favorable outcomes or were in remission at the time of publication.
Murphy, Brian G., et al. "The nucleoside analog GS-441524 strongly inhibits feline infectious peritonitis (FIP) virus in tissue culture and experimental cat infection studies." Veterinary microbiology 219 (2018): 226-233
Summary: Pharmacokinetic study to determine possible effective dosage of antiviral GS-441524.
FIP Diagnostic Flow Chart
Summary: Dr. Diane Addie conducts FIP research at the University of Glasgow. Her diagnostic algorithm comes from her 2009 paper (linked below), and can be used to help diagnose cats that may have effusive or non-effusive FIP.
(Link) Addie, Diane, et al. "Feline infectious peritonitis. ABCD guidelines on prevention and management." Journal of Feline Medicine & Surgery 11.7 (2009): 594-604.
Blood Test Template
Summary: A google sheet that can be duplicated and shared to help track FIP-relevant blood-test information. This is useful for understanding how a cat is responding to treatment, and when GS-441524 treatment may be stopped
GS-441524 is not presently licensed for distribution, manufacturing, or sale. It has also not been approved for treatment of FIP by any regulatory body. Given these concerns, there are currently no retail outlets that can sell the drug without potentially facing large liabilities. Given demand for GS-441524 for treating cats with FIP, however, a market has emerged. Manufacturers are located in China, and many individuals and groups have been working hard to setup supply chains to import GS-441524 into most countries in the world. There are several Facebook groups that exist which can help you gain access to GS-441524 to help treat your cat. A small subset of groups are listed below, that can help you find GS regardless of your cat's condition/location:
- The current published treatment recommendation is to treat cats for 84 days (12 weeks), daily with GS-441524 (Reference)
- Bloodwork and other clinical markers should be regularly monitored as treatment may need to be extended beyond 12 weeks (Reference)
- The published research on treating cats using GS-441524 uses a once-daily injection (Reference)
- Various doses are used to treat cats depending on the cat's symptom severity and weight (Reference). See discussion in dosage information below.
- Several Chinese companies have created an oral form of GS. The oral form has been used to successfully treat cats.
- There are not presently any peer-reviewed publications that document the efficacy of using oral GS, although admins from Facebook groups indicate that many cats have had great treatment outcomes. There is evidence in the peer-reviewed literature that the oral form can stop fecal shedding of Feline Coronavirus (Reference)
- Dr. Pedersen, the researcher from UC Davis that first discovered the efficacy of using GS-441524, has cautioned against using oral GS when treatment dosage reaches 10 mg/kg or higher.
The 84-day treatment recommendation originally comes from the 2018 GC376 paper,
in which cats were treated with different concentrations and for different durations of time using GC376. One cat, in particular, was found to relapse when treated for durations of time
less than 12-weeks. The 2019 study monitored PCV, serum total protein, globulin and albumin levels,
as well as the A:G ratio using regular blood tests for the enrolled cats. These values were identified as useful markers
affiliated with active FIP. Based on these markers, it appeared that cats had not completely recovered from FIP after 6–10 weeks of treatment,
which further helped support the 12-week minimum treatment period. The authors of these studies have also noted that the 12 week period is consistent with the
amount of time required to treat humans with HCV using protease inhibitor.
The 2019 study had a relapse rate of 30% when treating cats initially with 2 mg/kg of GS-441524. Many of the cats that relapsed in the original study were then treated for an additional 12 weeks at a higher dosage of 4 mg/kg. Most cats treated at 4 mg/kg did not relapse again. Several of the cats that relapsed the first time began to show neurological symptoms as the virus had moved past the blood brain barrier. From the 2020 study, it was found that neurological symptoms could be successfully treated with a higher dosage of GS than was used in the 2019 study. Dosages of 5 mg/kg to 10 mg/kg were investigated, and efficacy was shown in treating one neurological cat with a 10 mg/kg dosage.
The cats used for these studies were extensively screened, and are unlikely to be representative of the average cat presenting with FIP. As such, the dosage used for cats in these papers may or may not successfully treat your cat and its symptoms. Given the small sample size reported, it is difficult to generalize dosing recommendations.
At this time, many FIP treatment groups recommend a starting dosage of 6 mg/kg without additional information. Some admins recommend starting with higher initial dosage for serious cases to more rapidly stabilize your cat. Cats presenting with neurological or ocular symptoms are more likely to relapse, and may require a dosage higher than 6 mg/kg.
As cats become healthier from treatment, however, it becomes more difficult for the drug to penetrate the blood brain barrier, which suggests higher doses will be necessary if the virus has made it past the blood brain barrier. FIP is more likely to have entered the brain in dry-FIP cases and in relapse cases (reference).
GS-441524 treatment is not cheap. Due to its current status as an unregulated drug, costs are unlikely to be covered by insurance.
Treating your cat can be very expensive, outcomes can be uncertain, and your own financial situation may impact your decision to pursue treatment. Costs for the compound typically range from as little as $1 per mg to almost $4 per mg, resulting in cost ranges from $1,500 to over $9,000 to treat cats. Vet fees will likely add substantial additional costs as well. As all cats are different sizes, and all cats have different infection severity, different treatments decisions will be required for each cat.
This site contains a cost estimator to help you estimate the cost of treating your cat. This is an initial estimate, and actual treatment costs will be different. For this calculator, it is assumed that dry-FIP cases are treated at 10 mg/kg, and wet-FIP cases are treated at 6 mg/kg. The gain in cat weight is estimated based on actual data that has been logged on this website from cats undergoing treatment.
Dry FIP can be difficult to diagnose. It can take a long time for the disease to progress to a level where you and your vet can confirm FIP. As such, many cats may have been infected for a substantial durations of time, which means that it is more likely that the virus has moved past the blood brain barrier.
If the virus has progressed to this point, neurological or ocular symptoms are likely (reference). For dry FIP cases, however, it is not always clear if a cat is suffering from neurological symptoms. Many neurological symptoms can be subtle, and may be exceptionally hard to diagnose. Many dry FIP cats have experienced relapses due to undiagnosed neurological symptoms. Neurological symptoms can be treated using GS-441524, but for these cases, higher dosage (10 mg/kg) may be required to achieve long-term remission of the disease (reference).
There is only one peer-reviewed study that has been published that has shown successful treatment of Neurological FIP using GS-441524. Furthermore, this study only looked at treatment outcomes for 4 cats. As such, there is very limited data that is publicly available for assessing treatment outcomes and approaches for dealing with Ocular and Neurological forms of FIP.
For the small sample of cats treated in the study, there were positive outcomes for cats with as little as 5 mg/kg dosage of GS. However, relapses occured for other cats in the study even at this dosage. A higher dosage at 10 mg/kg was able to treat one cat that relapsed in the study. Many of admins in the Facebook groups have started suggesting treatments for Neurological and Ocular cases at dosage substantially above 10 mg/kg. If relapses occur for these cats, then further increases will likely be necessary to yield successful treatment outcomes.
Given the high dosages that are likely necessary to treat cats with Neurological and Ocular symptoms, treatment costs can be very high. Because there is limited data on treating cats with Neurological and Ocular forms of FIP, it is not known, at this time, what the long-term success rate is likely to be. With that said, many individuals treating for Neurological and Ocular FIP have reported positive outcomes.
Dr. Pedersen, the researcher from UC Davis that first discovered the efficacy of using GS-441524, has cautioned against using oral forms of GS when treatment dosage reaches 10 mg/kg or higher.