This site contains links to relevant peer-reviewed studies associated with using GS-441524 to treat cats for FIP. Short summaries are provided that can help you and your vet better understand the FIP treatment process and its efficacy, as well as other considerations and concerns for treating your FIP-positive cat.

Page Content

  1. Scientific Literature on GS-441524 and treating cats with FIP
  2. Diagnosing and Monitoring FIP
  3. How can I buy GS-441524?
  4. What does treatment look like?
    1. Treatment Duration
    2. Dosage and Cost
    3. Non-Effusive (dry) FIP Considerations
    4. Neurological and Ocular FIP Considerations
  5. Drugs to avoid
  6. Some useful resources


Relevant Peer Reviewed Research

Useful Information for Diagnosing and Monitoring FIP
  • 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

    For bloodwork, the above template contains the main indicators affiliated with FIP. These values should be monitored closely by you, your vet, and your warrior admin. Usually, extending treatment past 84 days is based on Albumin and Globulin levels, as well as the %LYM (which should be 30% or higher for discontinuing treatment), as well as other clinical indicators. For cats with Neurological FIP, bloodwork may not always be a reliable indicator as the virus will have passed the blood-brain barrier. This template provides additional information related to the high/low indication for the various bloodwork components of interest for diagnosing and assessing FIP


Obtaining GS-441524 for Treatment

GS-441524 is not presently licensed for distribution, manufacture, 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, and the patent on GS-441524 is not set to expire until November 2029.

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. 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. These groups can help you find GS regardless of your cat's condition/location:


Summary of the treatment process

Note: It is important to keep in mind that there is a lack of transparent, clinical data affiliated with treating cats for FIP. The studies that have been published use a relatively small sample of cats. The cats used in these studies were thoroughly vetted before being included in the study. FIP Warriors and other facebook groups have their own process for tracking treatment outcomes and making recommendations. There has not been good, standardized data collection across groups. This site hopes to improve and standardize data affiliated with treating cats for FIP. Even without good data, we do know that thousands of cats with FIP have been successfully treated with GS-441524, and that most of these cats have remained free of symptoms after being treated (now several years free of symptoms for some of earliest cats that were treated).
Treatment Duration and Information
  1. The current published treatment recommendation is to treat cats for 84 days (12 weeks), daily with GS-441524 (Reference)
  2. Bloodwork and other clinical markers should be regularly monitored as treatment may need to be extended beyond 12 weeks (Reference)
  3. The published research on treating cats using GS-441524 uses a once-daily injection (Reference)
  4. Various doses are used to treat cats depending on the cat's symptom severity and weight (Reference). See discussion in dosage information below.
  5. Several Chinese companies have created an oral form of GS. The oral form has been used to successfully treat cats.
  6. 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)
  7. 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.

Treatment duration after relapse
Cats that relapsed in the 2019 study relapsed within 3-84 days (average of 23 days) after the initial treatment. A set duration of time has not been officially established in the literature for treating kittens that have relapsed, especially if they are treated at higher dosage than was used in the study. For most relapse occurances, the authors treated the cats for an additional 12-weeks, or longer, at substantially higher dosage compared to the initial treatment. Shorter durations were used in some cases due to possible GS-441524-related side-effects(Reference)
GS-441524 dosage and costs
It is recommended that you work with an admin from one of the FIP treatment groups to determine what is likely to work best for you and your cat.

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, and lower dosage for other cats in the study.

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).

Costs

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 have been logged on this website from cats undergoing treatment.

Non-Effusive (dry) FIP Considerations

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. The data analysis on this website suggests that most Dry FIP cases have neurological involvement.

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 or higher) may be required to achieve long-term remission of the disease (reference).

Neurological and Ocular FIP Considerations

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.


Drugs to avoid
  • L-lysine: L-lysine should never be given to a cat with Fe-CoV infection or FIP because it is antagonistic to arginine which is essential for immune function.

  • Steroids after stabilization: Supportive (symptomatic) treatment may be needed during the initial illness to keep cats alive long enough for antivirals to have their effect. The drugs often include anti-inflammatories (corticosteroids, NSAIDS). It is best to avoid overuse of these drugs except on a temporary basis and only if there is strong justification for them, especially in severely ill cats for the first few days.

    The most important goal for treating FIP is to stop virus replication in macrophages, which will immediately halt the production of the numerous inflammatory and immunosuppressive cytokines that cause FIP signs. While some drugs such as corticosteroids (prednisolone) or NSAIDS (meloxicam) may inhibit inflammatory cytokines, the only drug that will completely inhibit these harmful cytokines are antiviral drugs such as GS-441524 or GC376. These drugs will cause dramatic improvements in fever, activity, appetite, etc. within 24-48 h. This improvement will be far greater than any achieved by other medications. Therefore, unless there is justification to use other drugs, they should be stopped as soon as a pronounced and steady improvement in FIP signs occurs.

    In addition to masking symptoms afiliated with FIP, steroids run the risk of interfering with the delivery of GS-441524 past the blood-brain barrier. It has been shown in some studies that steroids can inhibit the permeability across the blood-brain barrier (reference). Reduced permeability may decrease the effectiveness of GS-441524, and increase the risk of relapse in cats.

  • Some Antibiotics: The fluoroquinolone class of antibiotics such as Baytril/Enroflaxin, Zeniquin, Veraflox/Pradofloxacin and Orbax have fluorine so they can get into the brain/nervous system. Because of that, their side effects can cause neurologic symptoms. Since we are treating very sick kitties, we want to try not to add new symptoms that could confuse treatment when possible. If your veterinarian determines a fluoroquinolone antibiotic is needed, please follow their direction as there are some infections that must have this class of antibiotic

    The following antibiotics are okay for use to treat secondary infections:
    Zithromax, Cephalosporins (aka Convenia [injectable at vet], Cephalexin, Cefovecin, others), Amoxicillin, Penicillin, Clavamox/Augmentin, Doxycycline, Clindamycin (aka Clindacin, Clindamed, Clindamax and Zydaclin)

  • Drugs that may impact the CNS: FIP can move across the blood-brain barrier. Once it does, it can be very difficult to treat cats (neurological and ocular cases). Cats that have been infected for longer durations of time are more likely to manifest neurological symtpoms, indicating that the virus has entered the brain. This is the case for most Dry-FIP cases (reference). Drugs that impact the Central Nervous System may impact permeability across the blood-brain barrier, which could reduce the effectiveness of FIP treatment.


Additional Resources: