Clinical treatment

FIP Cats and GS-441524: A Ray of Hope in the Battle Against Feline Infectious Peritonitis

We’ve witnessed the heartache that Feline Infectious Peritonitis (FIP) can bring to cat owners. The diagnosis of this complex viral disease is often met with worry, confusion, and emotional turmoil. However, amidst the challenges, there’s a glimmer of hope in the form of GS-441524, an antiviral drug that has emerged as a beacon of possibility in the realm of FIP treatment.

Feline Infectious Peritonitis: A Complex Viral Disease

FIP is a formidable adversary. It can manifest in various forms, with symptoms ranging from fever and lethargy to weight loss and fluid accumulation in the abdomen or chest. Cat owners often find themselves navigating a maze of uncertainty when their beloved feline companions receive an FIP diagnosis.

The Role of GS-441524 in FIP Treatment


Amidst the adversity, GS-441524 shines as a potential game-changer in the fight against FIP. This antiviral drug holds the promise of combating the FIP virus and providing afflicted cats with a chance at a better life.

GS-441524 is an adenosine nucleotide analog antiviral, similar to remdesivir. This molecule was patented in 2009 by Gilead Sciences. In vitro studies of GS-441524 have determined it has a higher EC50 than remdesivir against a number of viruses, meaning GS-441524 is less potent. Remdesivir and GS-441524 were both found to be effective in vitro against feline coronavirus strains responsible for feline infectious peritonitis (FIP). Remdesivir was never tested in cats, but GS-441524 has been found to be effective treatment for FIP and is widely used despite no official FDA approval due to Gilead’s refusal to license this drug for veterinary use.

While GS-441524 isn’t a guaranteed cure, its use in treating FIP is backed by research and clinical trials. This gives cat owners a ray of hope and a potential path towards better health for their furry friends.

Anti Virus Mechanism of GS-441524

Intracellular triple-phosphorylation of GS-441524 yields its active 1′-cyano-substituted adenosine triphosphate analogue, which directly disrupts viral RNA replication by competing with endogenous NTPs for incorporation into nascent viral RNA transcripts and triggering delayed chain termination of RNA-dependent RNA polymerase.

Tolerance of GS-441524

In vitro experiments in Crandell Rees feline kidney (CRFK) cells found GS-441524 was nontoxic at 100 µM concentrations, 100 times the dose effective at inhibiting FIPV replication in cultured CRFK cells and infected macrophages. Clinical trials in cats indicate the drug is well-tolerated, with the primary side effect being dermal irritation from the acidity of the injection mix.

Some researchers suggesting its utility as a treatment for COVID-19 have pointed out advantages over remdesivir, including lack of on-target liver toxicity, longer half-life and exposure (AUC) and much cheaper and simpler synthesis.

Types of GS-441524 Formulations

GS-441524 is available in various formulations, each with its own set of advantages and considerations. These formulations include oral medications, injections, and other delivery methods.


Though GS-441524 is typically administered as an injectable solution, there are other formulations such as oral medications. GS-441524 oral form formulation is mostly available in tablet form. Tablet formulation strength varies from 5mg to 50 mg GS-441524 per pill. Cat owners may find the source on the FIP cat Facebook site or on Google. Just make sure the provider is reliable and the tablet strength is authentic.


GS-441524 was provided by Gilead Sciences as a pure and highly stable powder and diluted to a concentration of 10 or 15 mg/ml in:

  • 5% ethanol
  • 30% propylene glycol
  • 45% PEG 400 (polyethylene glycol)
  • 20% water with HCl to adjust the resulting pH to 1,5

The resulting mixture was shaken to dissolve in a sterile 50 ml flask and then placed in an ultrasonic bath for 5-20 minutes until it became completely clear. The drug thus dissolved was then stored in a refrigerator and used within 3-4 weeks.

The choice of formulation can impact the ease of administration and the effectiveness of treatment. For example, some cats may tolerate oral medications better, while others may benefit from injections. Discussing the options with your veterinarian is crucial in determining the most suitable form of GS-441524 for your cat.

Potential Benefits and Risks of GS-441524 Treatment

The potential benefits of GS-441524 treatment are encouraging. Cats undergoing treatment may experience improved quality of life, including reduced symptoms and enhanced vitality. Success stories of cats achieving remission offer hope to cat owners facing the daunting prospect of FIP.

However, it’s essential to be aware of potential risks and side effects associated with GS-441524. Not all cats may respond the same way to the medication, and some may experience injection site reactions or other adverse effects. Close monitoring and open communication with your veterinarian are vital in addressing any concerns or challenges that may arise during treatment.

Cost Considerations

Managing the cost of FIP treatment with GS-441524 is a concern for many cat owners. The price of the medication can vary, and it’s essential to explore potential sources for obtaining it. Some cat owners have found success in purchasing from trusted online sources, while others may seek assistance from organizations that provide financial aid for veterinary treatments. This tool may help a little bit to estimate the GS-441524 treatment cost based on cats’s weight and FIP type

Balancing the financial aspect of treatment with the desire to provide the best care for your cat requires careful consideration and planning.

Real Stories: Successes and Challenges

To shed light on the real-world experiences of cat owners facing FIP, let’s delve into some stories of hope and resilience. These anecdotes highlight not only the successes but also the challenges that cat owners may encounter during treatment.

Jane’s Story:* Jane’s cat, Whiskers, was diagnosed with the wet form of FIP. After discussing treatment options with her veterinarian, Jane decided to pursue GS-441524 injections. The journey wasn’t without its difficulties, including initial injection site reactions and the stress of administering daily injections. However, with unwavering dedication and support from her veterinarian, Jane saw gradual improvements in Whiskers’ health. Over time, the fluid accumulation in Whiskers’ abdomen decreased, and he regained his playful spirit. Jane’s story showcases the importance of persistence and the positive outcomes that can result from GS-441524 treatment.

Mark’s Challenge:* Mark’s cat, Luna, was diagnosed with the dry form of FIP. Luna was a particularly challenging patient, often resisting medication and displaying signs of anxiety during the injection process. Mark’s veterinarian recommended adjusting the treatment plan to include a compounded liquid formulation of GS-441524, which Luna found more palatable. While the journey was still filled with ups and downs, Mark’s determination and his veterinarian’s guidance eventually led to a noticeable improvement in Luna’s condition. Mark’s experience highlights the importance of flexibility and finding the right treatment approach for each cat’s unique needs.

Last: Hope and Support for FIP Cats

In the face of FIP, cat owners are not alone. GS-441524 represents a ray of hope, offering the potential for improved quality of life and even remission for cats afflicted by this challenging disease. While the journey may be marked by challenges, uncertainties, and financial considerations, the unwavering commitment of cat owners, combined with the guidance of veterinary professionals, can pave the way for better health and happiness for their beloved feline companions.

Remember, you are your cat’s advocate and source of support. Your dedication and love play a pivotal role in your cat’s transformative journey toward health and happiness.

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FIP Cat Treatment: The Life-Saving Information

I. Introduction

Feline Infectious Peritonitis (FIP) is a complex and often misunderstood disease that affects cats. We’ve seen firsthand the confusion and distress it can cause among cat owners. This article aims to shed light on FIP and its treatment, providing comprehensive information that you may not always receive from your vet. It’s a journey of understanding, a journey of hope, and a journey of love for our feline friends.

II. Understanding FIP in Cats

What is FIP?

FIP is a viral disease caused by certain strains of the feline coronavirus. It’s an aggressive disease that can affect cats of all ages, but it’s more common in young cats and kittens. The virus can mutate in the cat’s body, leading to an immune response that results in inflammation in various parts of the body. This inflammation can cause a wide range of symptoms and complications, making FIP a serious and often fatal disease.

Feline infectious peritonitis virus

Types of FIP

FIP can manifest in three forms: wet (effusive), dry (non-effusive) and neuro/ocular FIP

  • Wet FIP is characterized by the accumulation of fluid in the abdomen or chest, leading to breathing difficulties and a distended abdomen.
  • Dry FIP involves granulomas—small collections of inflammatory cells—in various organs. These granulomas can interfere with the function of the affected organs, leading to a wide range of symptoms.
  • There’s also a form that affects the brain and nervous system, known as neurological FIP, which can cause neurological symptoms such as seizures and loss of coordination.
Summary of the systemic clinical signs and pathologies associated with FIP. FIP is well known to be a systemic infection with a diverse presentation. From httpss://

Symptoms of FIP

Symptoms of FIP can vary widely and may include fever, weight loss, loss of appetite, and lethargy. Wet FIP often causes a distended abdomen due to fluid accumulation, while dry FIP symptoms depend on the organs affected. For instance, if the liver is affected, the cat may become jaundiced, while lung involvement may cause breathing difficulties. Neurological FIP can lead to changes in behavior, seizures, and loss of coordination. It’s important to remember that these symptoms can also be seen in many other diseases, which is why FIP can be difficult to diagnose.

III. The Diagnosis Process

Challenging to Diagnose FIP

Diagnosing FIP can be challenging due to its nonspecific symptoms. Vets often rely on a combination of clinical signs, blood tests, and analysis of any accumulated fluid. For instance, a blood test may reveal anemia and increased proteins in the blood, while analysis of the fluid from wet FIP may show high protein levels and specific types of cells. However, these findings are not exclusive to FIP and can be seen in other diseases as well.

FIP is often misdiagnosed because its symptoms can mimic other diseases. I remember a case where a cat was initially diagnosed with liver disease due to jaundice and weight loss. However, further testing revealed it was actually suffering from dry FIP. This highlights the importance of comprehensive diagnostic testing in ensuring an accurate diagnosis.

The Importance of a Second Opinion

Given the complexities of diagnosing FIP, it’s crucial to seek a second opinion if your cat’s condition doesn’t improve or worsens despite treatment. A second opinion can provide a fresh perspective and may uncover aspects of the case that were initially overlooked. It’s always better to have more information when dealing with a disease as complex as FIP.

IV. Treatment Options for FIP

Traditional Treatment Options

Traditional treatment for FIP is mainly supportive and includes fluid therapy to address dehydration and anti-inflammatory drugs to control inflammation and fever. Fluid therapy can help replace the fluids lost due to vomiting, diarrhea, or lack of appetite, while anti-inflammatory drugs can help reduce the inflammation caused by the disease. However, these treatments do not address the underlying cause of the disease and are mainly aimed at improving the cat’s quality of life.


A 2018 study published by Murphy et al. demonstrated that GS-441524, a less chemically complex parent nucleoside (also patented by Gilead), was highly effective against experimentally induced FIP at a dosage of 4.0 mg/kg subcutaneously every 24 h for 12 weeks (84 days) in 10 laboratory cats. This gives us hope to treat FIP cats.

Experimental Treatments and Clinical Trials

There are ongoing clinical trials exploring new treatments for FIP. Participating in these trials can provide access to cutting-edge treatments and contribute to our understanding of the disease. I’ve had patients who have participated in these trials, and while it’s not a guarantee of a cure, it does offer hope for a potential breakthrough in FIP treatment.

V. What Vets Don’t Often Tell You

The Reality of FIP Prognosis

FIP is often considered fatal, but it’s important to remember that every cat is unique, and some do respond well to treatment. I’ve seen cases where cats with FIP have lived for months or even years with a good quality of life. While it’s important to be realistic about the prognosis, it’s equally important to maintain hope and celebrate every moment with your beloved pet.

The Cost of FIP Treatment

The cost of GS-441524 formulation to treat Feline Infectious Peritonitis cats can vary widely depending on several factors.

  • Dosage and Treatment Duration: The cost of GS-441524 is often calculated based on the required dosage and the duration of treatment. Cats with FIP may require treatment for several weeks or even months. The longer the treatment duration and the higher the dosage, the more expensive the treatment can be.
  • Concentration of the Medication: GS-441524 may be available in different concentrations, and the cost can vary depending on the concentration used. Higher concentrations may be more expensive but can also allow for smaller volumes to be administered.
  • Source of the Medication: The source from which you obtain GS-441524 can impact the cost. Some cat owners obtain the medication through compounding pharmacies, while others may participate in clinical trials where the medication is provided as part of the study. The cost can also vary if you purchase it from a trusted online source.

FIP Doctor provides a website to calculate daily and monthly dosage and cost based on the type of FIP and weight.

The Emotional Toll of FIP

Dealing with a cat’s FIP diagnosis can be emotionally draining. I’ve seen many owners struggle with feelings of guilt, sadness, and anxiety. It’s crucial to seek support from friends, family, or professional counselors during this time. Remember, it’s okay to feel overwhelmed and it’s okay to ask for help. You’re not alone in this journey.

VI. Caring for a Cat with FIP at Home

Managing Symptoms at Home

Making your cat comfortable at home involves managing their symptoms. This can include providing a warm and quiet place to rest, encouraging them to eat, and giving them plenty of love and attention. I’ve had clients who’ve set up special areas in their homes for their cats, complete with heated beds and favorite toys. These small gestures can make a big difference in your cat’s comfort and well-being.

Dietary Considerations

Cats with FIP often lose their appetite, so it’s important to offer them palatable, high-quality food. Warming up their food or offering a variety can sometimes help stimulate their appetite. I’ve had clients who’ve had success with feeding their cats homemade meals, under the guidance of a veterinary nutritionist. It’s all about finding what works for your cat and providing them with the nutrition they need.

Regular Vet Check-ups and Early Detection

Regular vet check-ups can help detect any health issues early, including FIP. Early detection can lead to more effective management of the disease. I’ve had cases where early detection of FIP has allowed for early intervention and improved outcomes. It’s a testament to the importance of regular vet visits and proactive healthcare.

Preventing the Spread of FIP

In multi-cat households, it’s important to isolate a cat diagnosed with FIP to prevent the spread of the virus. Regular cleaning and disinfection are also crucial. I’ve had clients who’ve successfully managed to prevent the spread of FIP in their multi-cat households through diligent hygiene practices and careful management. It’s a challenging task, but it’s certainly possible with the right measures.

VII. Conclusion

Understanding FIP and its treatment can be a complex journey, but remember, you’re not alone. Stay informed, ask questions, and don’t lose hope. Feel free to reach out with any questions or share your experiences—we’re all in this together. And remember, every moment with your beloved pet is precious. Cherish them, love them, and know that you’re doing your best for them.

Remember, this article is intended to provide general information about FIP and its treatment. Always consult with your vet for advice tailored to your cat’s specific situation.

Niels C. Pedersen FIP Cat GS-441524

GS-441524 treatment & dosage

Niels C. Pedersen, Nicole Jacque

September 24, 2021


The initial field testing of GS-441524 for FIP treatment involved subcutaneous injection. This route of administration was based on prior pharmacokinetic (PK) studies done on laboratory cats. Intravenous and subcutaneous routes of injection yielded similar high blood levels that were sustained at virus inhibitory concentrations for over 24 hours. Oral administration was also found to provide blood levels, but somewhat delayed and only at about 40% peak levels of subcutaneous and intravenous routes (Pedersen NC, unpublished data, 2018). However, dogs which have a longer intestinal tract evolved for omnivorous diets, can absorb up to 85% of GS441524 by the oral route [1, 5]. Dogs have often been used as surrogates for humans in oral absorption studies, so oral absorption in humans is also likely to be higher than in cats. Therefore, the subcutaneous route was chosen for field testing in cats based on ease of administration and resulting blood levels.

Current brands of capsules/tablets are sold as supplements and their labels list several common innocuous chemical compounds and medicinal herbs and do not list GS-441524 as one of the ingredients. This is probably done to avoid scrutiny by customs. Regardless of the list of ingredients, the active component in all oral products is GS-441524. The exact concentration of GS-441524 in the various oral products is kept secret by the sellers, but it is obviously several times higher than would be needed if the drug were given by the subcutaneous route.

We were initially critical of the oral route for two reasons. First, oral forms were more wasteful of what was initially a rare and expensive resource. Second, published research on oral absorption of nucleosides (GS-441524 is a nucleoside) document a concentration limit or ceiling for oral absorption [2-5]. This limitation would make it theoretically difficult to achieve the extremely high blood concentrations required to treat certain forms of FIP (e.g., neurological) and/or to overcome the problem of acquired drug resistance. Newer information obtained from field use of the oral forms of GS-441524, indicate that this problem may not be as serious as first believed as most forms of FIP respond equally well whether given pills or injections.

It appears that more and more owners and veterinarians are embracing oral GS-441524 for part or all the treatment. The cost of oral GS-441524 preparations has steadily declined over the last two years and quality increased. The problem of injection site reactions, coupled with more effective oral preparations of GS-441524, have encouraged the oral treatment. Steadily increasing numbers of cats are being treated with oral drug either for part or all of the treatment.

Formulation and Dosing

Suppliers of oral GS-441524 do not list the amount of active drug in their tablets or capsules. Some suppliers also provide pills with a higher concentration of GS-441524 for use in cats with ocular and neurological FIP to limit pills that must be given at one time. In addition, one supplier has tablets labeled for administration every 12 hour (h) and yet another for every 24h. The 1 tablet/kg q12 h tablet contains one half as much GS-441524 as a 1 tablet/kg q24h tablet the rationale being that the q12h dosing would prevent a fall-off in the blood concentration prior to 24h. This belief is inconsistent with the original pharmacokinetic data, which shows blood levels to be sustained at effective levels for at least 24h. Regardless, both the q12h and q24h pills seem equally effective when given according to instructions, although most owners prefer dosing once a day.

FIP Doctor Oral tablet dosage recommendation

Form of FIPDosageKittab 10 q24h
(10mg GS-441524)
Kittab 25 q24h
(25mg GS-441524)
Kittab 50 q24h
(50mg GS-441524)
Wet6 mg/kg0.6 tablet/kg0.25 tablet/kg0.12 tablet/kg
Dry8 mg/kg0.80.30.16
Ocular10 mg/kg10.40.2
Neurological12 mg/kg1.20.50.24


All oral brands have similar instructions for administering capsules or tablets. Fasting for half an hour before and after giving the medication is generally recommended. A small amount of treat may encourage cats to take them, and many cats will consume them when put on a plate with a coating treat.


The price of oral GS has significantly decreased in the last year. Nevertheless, the relative cost of oral GS-441524 is 20-40% higher (depending on the supplier) than their injectable version. Cost calculator may help cat owners to estimate the daily or monthly cost.

Factors affecting oral vs. injection

Cats currently experiencing vomiting/regurgitation and diarrhea are generally considered poor candidates for oral GS-441524. Therefore, cats with serious gastro-intestinal disease are often started on injections, at least until the problems are resolved. Most people, especially in the past, have started with injectable GS-441524. The injection form is cheaper, and the dosage is more accurately managed. Absorption of GS-441524 is also more reliable by the subcutaneous than oral route, which is often a critical factor in the initial treatment of cats that are severely ill and unstable at the onset. Whether or not a cat continues injectable GS-441524 is often conditioned on the ability of the owner to do injections in the most effective manner, the willingness of the cat to adapt to the injection pain, and the occurrence of injection site sores. Oral medication is often a welcome respite for owner and feline patient in such situations.

Comparison of treatment success between injectable and oral GS-441524

Assuming that dosages are accurately calculated, and dosing properly done, the success rate with oral GS-441524 currently mirrors that of injectable formulations. Nevertheless, differences in responses between oral and injectable GS-441524 have been reported. A small number of cats have not responded well to oral GS-441524 as initial treatment or have led to relapses when replacing injections. Alternatively, switching cats to oral GS-441524 at an equivalent dosge has resolved disease that was not responding well to injections. It is difficult to assign these dramatic differences in response to the drug form, as GS-441524 given by subcutaneous or oral routes ends up in the bloodstream and ultimately in the tissues. It is more likely that the brands of injectable or oral GS-441524 used prior to such switching were not good. Indeed, there have been many cases when switching to a different oral or injectable brand immediately improved the response.

It was assumed that only the injectable form of GS-441524 could achieve the extremely high blood and cerebrospinal fluid levels necessary to effectively treat neurological disease, especially in situations where the virus has evolved variable degrees of drug resistance. However, oral brands such as Aura/Lucky have been quite effective on cats with neurological FIP. This has also included some cats who were failing to respond to an extremely high dosage of injectable GS441524. More and more cats with neurological FIP are being cured with entirely oral treatment. This is either due to more experience with oral treatment in difficult cases of FIP, or equally likely, to the increased quality of oral formulations.

Summary of currently available brands of oral GS-441524

Information on oral forms of GS-441524 is sparse regarding treatment outcomes but there are a growing number of brands that are available, attesting to the popularity of this form of treatment. Information on these brands is updated at the FIP Warrior CZ/SK website [7]. This website also contains excellent information on FIP and GS-441524 treatment.

The recommended dosages vary from brand to brand and do not always correspond to the equivalent dosage for injectable GS-441524. GS-441424 is absorbed from the intestine with about 50% efficiency as subcutaneous or intravenous administration. There is also a theoretical upward limit to absorption through the intestine, which would also limit the blood levels that can be obtained. Given the absorption limitations of oral GS-441524, one would expect the oral dosage to be around twice that of injections. However, most oral brands are recommended at an equivalent dosage to injections. This suggests that the actual concentration of GS-441524 in oral preparations may be higher than for injectable GS-441524 as listed in the tables below and as provided by the FIP Warrior CZ/SK website.

Referenced studies on GI absorption of nucleosides related to GS-441524 and GS-441524


1. Thomas L. A precursor to remdesivir shows therapeutic potential for COVID-19.

2. Painter GR, Bowen RA, Bluemling GR, et al. The prophylactic and therapeutic activity of a broadly active ribonucleoside analog in a murine model of intranasal venezuelan equine encephalitis virus infection. Antiviral Res. 2019; 171:104597.  doi: 10.1016/j.antiviral.2019.104597

3. Cass, C.E., Young, J.D., Baldwin, S.A., Cabrita, M.A., Graham, K.A., Griffiths, M.,Jennings, L.L., Mackey, J.R., Ng, A.M., Ritzel, M.W., Vickers, M.F., Yao, S.Y., 1999.Nucleoside transporters of mammalian cells. Pharm. Biotechnol. 12313–12352

4. de Miranda, P., Krasny, H.C., Page, D.A., Elion, G.B., 1981. The disposition of acyclovir indifferent species. J. Pharmacol. Exp. Ther. 219 (2), 309–315

5. Vijayalakshmi, D., Belt, J.A., 1988. Sodium-dependent nucleoside transport in mouse intestinal epithelial cells. Two transport systems with differing substrate specificities. Biol. Chem. 263 (36), 19419–19423.

6. Yan VC, Khadka S, Arthur K, Ackroyd JJ, Georgiou DK, Muller FL. Pharmacokinetics of Orally Administered GS-441524 in Dogs. bioRxiv, doi: httpss://

7. FIP Warriors CZ/SK, httpss://

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