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Revolutionizing Feline Health: The Power of GS-441524 in Treating Feline Infectious Peritonitis (FIP

Updated: Jan 18

What Causes Feline Infectious Peritonitis?

Feline infectious peritonitis, caused by feline coronavirus, shares its name with the virus that causes human coronavirus (COVID-19), which may cause concern for some individuals. However, it is important to note that unlike human coronavirus, feline coronavirus is only transmitted between cats and is typically not harmful. The benign form of the virus is called feline enteric virus (FECV) and is commonly observed in cats, causing mild diarrhea that can be easily treated by veterinarians.

Unfortunately, in approximately 2% of cases, the feline coronavirus can mutate into the more deadly feline infectious peritonitis virus (FIPV), which is nearly always fatal. FIP can affect cats of all ages, and while various drugs such as interferon Omega, immunomodulators, immunosuppressants, steroidal anti-inflammatory drugs, and antibiotics have been used to treat FIP, they only manage the symptoms rather than targeting the root cause of the disease.

More recently, the antiviral drug GC376 was tested and initially showed promise in treating FIP in a clinical study. However, subsequent trials found it to be ineffective in a high percentage of FIP cases, as well as in treating relapse cases. As of now, an effective treatment for FIP remains a challenge for both cat owners and veterinarians.

Clinically Effective FIP Treatment | GS441524

A major breakthrough in veterinary science was achieved when Dr. Niels Pedersen and a team of researchers at the University of California Davis, conducting FIP research, decided to repurpose a human antiviral drug for FIPV treatment. Their idea was successful, as they treated 31 cats for 12 weeks and achieved an efficacy rate of 83%, providing a much-needed solution for desperate cat owners worldwide.

The drug used in this treatment is called GS441524, which has been found to be equally effective in treating both effusive feline infectious peritonitis (wet FIP) and non-effusive feline infectious peritonitis (dry FIP). This discovery was a significant advancement in veterinary medicine, and subsequent clinical trials conducted globally on cats with naturally acquired FIP and experimentally infected FIP have confirmed the UC Davis team's results. Consequently, a growing awareness of the nucleoside analog GS441524 and its effectiveness in treating feline infectious peritonitis in cats is emerging amongst cat owners and medical practitioners worldwide.

GS441524 is administered through subcutaneous injections and works by inhibiting FIPV replication. Treated cats demonstrate visible signs of recovery in as little as 3-4 days, in addition to eliminating common clinical signs such as fever, lethargy, lack of appetite, and abdominal swelling. Moreover, GS441524 has been found to be equally effective in eliminating neurological signs of seizures and physical paralysis. Additionally, GS441524 can serve as a diagnostic tool for FIP infection.

Although GS 441524, an antiviral drug for treating Feline infectious peritonitis, is still pending approval from the Food and Drug Administration (FDA) in the USA and other countries, it is available for purchase through unregulated sources on the internet. These sources are often referred to as black market suppliers. Here are some examples of where to find the drug:

  • Established in 2019, was the first website to offer online ordering of GS 441524. It has fast and efficient service, with knowledgeable and helpful customer support.

  • This was one of the first reputable brands to enter the market after Dr. Niels Pedersen's clinical study was published. was also the first company to introduce the oral form of GS 441524.

  • Facebook Groups: FIP Warriors and FIP Fighters are two of the largest groups in the USA, and FIP Free is the largest group in Germany. These groups may offer information on where to find GS 441524.

Today, finding FIP online self-help communities in your area is easy through a Google search. While Feline infectious peritonitis treatment is at the forefront of veterinary science in the 21st century, obtaining GS-441524 through unregulated sources poses risks for cat owners. It is important to note that the responsibility for obtaining the drug falls on the cat owners, who may encounter various sellers offering GS-441524, both reliable and unreliable. It is essential to choose a trustworthy brand or reseller.

BUYING FIP TREATMENT: 3 things you should know!

Choose reputation, not price.

Just like veterinarians, it is not recommended to purchase the cheapest drugs when looking for GS-441524 to treat FIP in cats. Unfortunately, there have been reports of cats dying during GS-441524 treatment due to the use of budget brands from unknown sellers. This is highly unusual given the proven effectiveness of GS-441524. Further investigation and testing revealed that these brands were overstating their GS concentration, with their claimed concentration of 15mg/ml actually being between 7-8mg/ml in some tests.

Additionally, these brands were found to have unstable formulations, with observable changes in pH level and viscosity from one production batch to another. Developing quality medicine requires knowledgeable chemists, precise instruments, high-quality chemicals, and consistent protocols, none of which can be obtained cheaply. As a result, it is unlikely that a reliable final product can be produced at a low cost.

Buy directly from the brand's website or its authorised resellers whenever possible.

Uncertain about whether the seller you're purchasing from is an authorized reseller? You can verify by contacting the brand through email. If the brand cannot be found online, it is better to avoid it entirely. Since GS is a costly treatment, there is an incentive for some unscrupulous resellers to dilute it with water or substitute one brand for another during delivery. This is not a frequent occurrence, but it has happened previously.

Talk to sellers who are knowledgeable about FIP

When purchasing a veterinary drug, it's not just about the product itself, but also the knowledge that comes with it. It's important to consider whether the seller is knowledgeable about the disease and the treatment, and whether they are transparent and forthcoming with information. Do they take the time to understand your cat's individual circumstances and potential complications during treatment? Ultimately, the seller's expertise and ability to provide clear and sensible information should be a significant factor in your decision-making process.

FIP Symptoms

Diagnosing FIP can be challenging, even for experienced veterinarians, due to its symptoms overlapping with other common illnesses. Since only a small percentage of cats worldwide contract FIP, vets often diagnose and treat for more common diseases when presented with ambiguous symptoms. It is only when FIP infection reaches an advanced stage, or after testing and treatments for other diseases, that vets may suspect FIP infection.

Currently, there is no definitive test for FIP diagnosis. Vets often need to perform multiple tests, some quick and inexpensive, while others are complicated and costly, to arrive at a confident diagnosis. Common external symptoms that can be observed with the naked eye include:

  • Lethargy

  • Lack of movement

  • Loss of appetite

  • Persistent fever

  • Yellowing of the gums or eyes, commonly called jaundice

  • Significant swelling in the abdomen

  • Physical paralysis

Internal symptoms, only observable with medical testing

  • low number of red blood cells

  • high number of white blood cells

  • elevated concentrations of protein in the blood

In the case of fluid build-up in your cat's chest or abdomen, your veterinarian may obtain a sample of the fluid for testing. The presence of yellow-tinged fluid with a high protein percentage is an indication of FIP. Your veterinarian may also perform an X-ray or ultrasound if FIP is suspected.

Other tests may also be useful in supporting a FIP diagnosis. For example, the immunoperoxidase test can detect white blood cells infected with the virus, while polymerase chain reaction technology can test for the virus in tissue or body fluids. In some cases, a biopsy of infected tissue inside the abdominal cavity may be necessary. Despite these tests' potential to support a veterinarian's diagnosis, none of them are 100% accurate.

Effusive Feline Infectious Peritonitis a.k.a. Wet FIP

FIP can manifest in a variety of symptoms as the virus spreads throughout the body, such as peritonitis with fluid accumulation in the abdomen, or in some cases, fluid accumulation in the chest cavity, inflammation of the brain, eyes, liver, kidneys, or other organs.

The effusive form of FIP is caused by inflammation of blood vessels (vasculitis) that can occur anywhere in the body, leading to protein-rich fluid leakage from damaged blood vessels and filling up various body cavities. The most common form of effusive FIP leads to fluid accumulation in the abdomen, which is why it was originally named "peritonitis."

Diagnosis of the effusive form of FIP is often easier due to visible signs such as bloating in the abdomen for fluid accumulation or laboured breathing in the case of pleural cavity fluid accumulation.

Non Effusive Feline Infectious Peritonitis a.k.a Dry FIP

The Non-effusive form of FIP is characterized by granulomatous inflammation, which is a specific type of inflammatory reaction incited by the FIPV virus. This results in the development of a ball of inflammation around the virus, causing damage to the surrounding tissue. Although any organ or body system can be affected, the central nervous system and eyes are the primary targets of FIPV.

Diagnosing the dry form of FIP in its early stages is challenging since symptoms are similar to those of other common feline diseases. The incubation period for the dry form of FIPV can last for over two weeks, during which cats appear outwardly healthy and normal. However, when symptoms start to manifest, it can quickly progress to late-stage infection, which is characterized by neurological disorders such as physical paralysis and seizures.

Diagnosing FIP in Cats

FIP can often be misdiagnosed as other more common diseases due to similar clinical signs, such as fever, weight loss, diarrhea, lethargy, cloudiness in the eyes, respiratory distress, and a swollen abdomen. Therefore, diagnosing FIP early is challenging and requires multiple tests and experienced veterinary expertise. Here are four commonly used tests by veterinarians to detect Feline Infectious Peritonitis Virus (FIPV) in cats. While no single test can conclusively diagnose FIPV, these tests can detect the virus antigen in body fluids and fecal matter and aid in determining the likelihood of FIPV infection when used in combination with clinical experience and expertise.

Titre test for cats
Titre test for cats

1. Titre Test

A titre test measures the level of antibodies circulating in the blood. These antibodies are produced when pathogens such as viruses or bacterias produce a response from the immune system. You can read more about the titre test here.

2. Histopathology

Doctors surgically collect and examine tissue samples. The pieces of tissue are prepared through a process called histology by preserving, thinly slicing or sectioning, and staining the tissue sample with dyes.

Tissue Sample taken from a FIP cat
Tissue Sample taken from a FIP cat

Once prepared, the tissue sections are examined under the microscope by a veterinary pathologist. Histopathology focuses on the architecture of the tissue.

The accuracy of a diagnosis is usually high. However, the downside is that it is slow and expensive. A veterinary pathologist can often offer an opinion on the likely course of the disease, called a prognosis. This information helps your veterinarian to decide the best course of treatment for your pet.

3. Rivalta Test

A simple yet useful test to determine the WET form of FIP. The test is performed by collecting sample fluid from the cat’s abdominal or chest cavity, adding it to a test tube filled with distilled water and one drop of 98% acetic acid. You can see a video of Rivalta Test performed here.

Rivalta test for effusive feline infectious peritonitis
Rivalta test for effusive feline infectious peritonitis

4. Blood Test

A comprehensive blood test is commonly used by veterinarians to determine the likelihood of a FIP viral infection in cats. In the CBC blood test doctors are looking for high white blood cell count and low red blood cell count. The biochemistry profile commonly reveals an increase in total protein and globulins. This increase indicates the inflammatory process as the cat's body responds to the virus. Veterinarians often look at A:G ratios as the first sign of potential FIP infection in cats.

Blood report: signs of FIP infection
Blood report: signs of FIP infection [Credit:]

This sample blood report shows an increase of Total Protein and Globulin (hyperglobulinemia) in a FIP positive cat.

Other tests on the biochemistry profile could, but not necessarily indicate FIP in cats since these problems could also occur with other diseases. For example, if the kidney values are increased in an older cat with suspicion of FIP, some of the possibilities are:

  • Chronic renal failure along with FIP (this cat has 2 different diseases)

  • Chronic renal failure with no FIP

  • FIP causing kidney disease

  • Dehydration due to FIP

  • Dehydration due to disease in some other organ

How to Prevent FIP?

The virus responsible for feline infectious peritonitis is not itself contagious, but the feline coronavirus (FCoV) that can lead to FIP is highly contagious. FCoV can be transmitted between cats through bodily fluids such as saliva and urine, as well as feces. FIP is more prevalent in multi-cat households, but even single cats can contract the virus from street cats or exposure at a rescue or breeding facility. While isolating a FIP-infected cat is recommended in multi-cat households, the virus may have already spread to and from other cats.

A quick FCoV test can be performed for your cat, and if the result is negative, we suggest getting them vaccinated for FIPV at your local veterinary clinic. Though the current FIPV vaccine is only about 50% effective, it still provides some protection and can reduce the risk of infection.

Keeping your cat indoors is also recommended, but if you do allow them outside, keeping them on a leash can prevent contact with saliva droplets, feces, and urine left behind by other animals that may carry the virus even after they've gone.


Our goal in providing this detailed FIP treatment guide is to help you gain a better understanding of the disease and effective treatment options. While we have covered many important aspects of feline infectious peritonitis in this article, there is still much more to learn. If you have any further questions about FIP or its treatment, please don't hesitate to contact us at

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