Feline Infectious Peritonitis (FIP): an in-depth look.

endFIP attention please Please note: this section is intended for individuals who want to learn more and have a deeper understanding of feline coronavirus and FIP. Basic knowledge of veterinary/scientific terms is needed to fully comprehend this section which was created for information purposes ONLY.

If you are a pet parent with a sick cat, please consult a qualified veterinarian IMMEDIATELY.

The authors exclude all liability whatsoever for any loss or damage arising out of the use of this website or reliance upon its content and STRONGLY advises anybody with veterinary-related questions to consult a qualified veterinarian. No responsibility can be accepted.

Treatment (Updated 06-2024)

FIP is caused by infection with feline coronavirus (FCoV). Coronaviruses are a common group of viruses that often infect the upper respiratory tract (nose and throat) or gastrointestinal tract (intestines) in different species. Covid-19 is caused by a novel coronavirus (SARS-CoV-2) and it is important to note that the coronavirus causing FIP is NOT the same and ONLY infects cats. FIP is a complex disease to diagnose. Historically, no effective treatment was available, so most cats with confirmed FIP died or were humanly euthanized, as FIP has a very poor prognosis. Sadly, until recently FIP was considered a fatal disease, with very few treatment options. Due to the Covid-19 outbreak, novel antiviral drugs have become available not just for humans but also for veterinary use.

Before treating the cat, every effort must be made to ensure a correct diagnosis. If an effusion is present, some cats benefit from the removal of the effusion, particularly if pleural effusions (fluids in the chest) are resulting in dyspnea (difficult or labored breathing). Effusions can often be removed with minimal restraint and without sedation. Abdominal or thoracocentesis will also remove virus-infected cells which are a source of pro-inflammatory cytokines. A small amount (1-2 ml in a plain tube) should be sent to a reputable laboratory for FCoV RT-PCR testing. If the result is positive, it confirms the diagnosis of FIP. If negative, other lookalike conditions of infectious etiology (such as septic peritonitis or pleurisy) should be considered, as the wrong treatment of the wrong disease could prove disastrous and even fatal.

Before even considering treatment for feline infectious peritonitis (FIP) you absolutely MUST ensure that the cat really does have FIP.

Because FIP is an immune-mediated disease, the treatment falls into two categories: Direct action against the virus itself and modulation of the immune response.



One of the silver linings of the Covid-19 pandemic is that it has put coronavirus firmly at the top of the priority list in countries around the world. The speed at which safe and effective coronavirus vaccines and therapies have been developed is nothing short of remarkable. FIP was previously fatal for most cats. However, in the last few years, significant developments have occurred in treatment. Recent research has shown that some newer anti-viral drugs such as GS-5734 and GS 441524 (used in humans against some emerging viruses), can be effective in the management of this once fatal condition.

A bit of background information:

Remdesivir, an antiviral medicine given to hospitalized Covid-19 patients through an IV obtained full FDA approval on October 22, 2020. The drug, which California-based Gilead Sciences Inc. is calling Veklury, had been authorized for use on an emergency basis since Spring 2020.

Therefore, since then, veterinarians had the authority to use it off-label — or “extra-label” in FDA parlance. Extra-label use of Veklury (Remdesivir) is permitted for the treatment of cats with FIP if that use is by or on the lawful order of a licensed veterinarian within the context of a veterinarian-client-patient relationship and is in compliance with the Extra- Label Drug Use regulations in the Code of Federal Regulations Title 21 part 530.

Remdesivir (GS-5734TM) is a broad-spectrum small-molecule antiviral drug that has demonstrated activity against RNA viruses. The drug was originally developed to treat Ebola virus infection, hepatitis C, and human Coronavirus disease. Remdesivir is a prodrug of the parent adenosine analog (GS-441524TM), containing an extra chemical side chain (including a phosphate group) that is supposed to improve intracellular penetration. It is common knowledge within the FIP community that GS-441524 has displayed antiviral activity against the feline infectious peritonitis causal pathogen. This has led to a growth in illegal supplies of these medications, sold to understandably concerned cat owners and caregivers. GS-441524 is one of a group of antiviral drugs which block the virus’ ability to make copies of its genetic material, essential for its spread and survival. Since 2021 a legal supply of both Remdesivir and GS-441524 has been available in the United Kingdom, Australia,  and via export to other countries.

Bova Specials U.K Ltd, a London-based Specials Manufacturer released Remdesivir as an extemporaneous preparation (also known as “veterinary special”) product to treat Feline Infectious Peritonitis (FIP) during the summer of 2021, and by the end of the year launched GS-441524 tablets. The 50mg tablets are known by their active pharmaceutical ingredient (API) and are quad-scored and tuna flavored. With the addition of the safe and legal GS-441524 tablets, Bova Specials U.K Ltd has placed itself at the forefront of the FIP treatment field.

Bova Specials U.K Ltd is producing this “veterinary special” formulation to treat FIP cats in a licensed Good Manufacturing Practice (GMP) facility which is audited by the Veterinary Medicines Directorate (VMD) and will sell directly to veterinarians (upon registering at in the U.K following the prescribing cascade.

Currently, Australia and the United Kingdom are the only countries where Remdesivir (a prodrug of GS441524) is readily available via prescription for veterinary use via BOVA Australia and Bova Specials U.K Ltd respectively. However, veterinarians in Canada, India, South Africa, and some parts of Europe, have also started accessing the drug-using human suppliers. It is worthwhile to note that black market products remain available, but of unknown content and safety thus legal drugs should be selected for the treatment of FIP. As well as helping pet parents and their cats, selecting legal treatments will help extricate practicing veterinary surgeons from a challenging professional position.

VETERINARY SURGEONS practicing in the U.K, and wishing to explore legal and safe options, or with general questions about FIP case management – Contact:

VETERINARIANS abroad can request information by contacting the export team at:


As Bova Specials U.K Ltd is based in the United Kingdom, their focus is on the U.K. population first, however, they will help anyone interested in importing this product. The process is a bit cumbersome and requires a considerable amount of paperwork. In addition, authorities in other countries may simply not like the import of products that do not hold a Marketing Authorisation (MA). If people in other countries want to import the Remdesivir formulation they need to:

• Get their veterinarian to contact Bova Specials U.K Ltd at:

• Veterinary surgeons need to provide proof of registration. UK is RCVS and it is different for each country, ideally a web address to show this from their governing body

• Veterinarians need to register the account and sort out the finance side and address, often they will get charged import taxes as well

• Fill out an order form and sign (the same signature of the veterinarian surgeons recorded on the Bova Specials U.K Ltd system, cannot be another veterinarian)

• Obtain proof it is legal for them to import Remdesivir from their authority. Veterinarians may just fill out some forms or they may need to provide further data (different countries have different regulations).

• When all of the documentation is ready, Bova Specials U.K Ltd can ship. They must have this before shipping as they are inspected by the Veterinary Medicines Directorate (VMD) and if any of this documentation is missing, they risk losing their license.


Please join us in the real call to action to help spread the word about this safe and legal FIP treatment option. As guardians of our beloved cats, we need to share this information broadly and effectively with our veterinarians and fellow cat parents. Additional information about these new treatments can be found HERE.

DO NOT contact Bova Specials U.K Ltd as they CAN’T speak to cat owners about any of their products nor provide pricing.


If you need assistance with the diagnosis and treatment of a suspected case of FIP, please email fipadvice@gmail.comThe “FIP advice” email address is managed by a group of highly qualified feline specialists based in the United Kingdom. These specialists have come together voluntarily and are available to assist veterinary surgeons and veterinary nurses by answering questions about FIP diagnosis and new treatments. Additional information about these new treatments can be found HERE.


Stokes Pharmacy, a leading compounding pharmacy, announced an exclusive partnership with the Bova Group to offer identical GS tablets to the ones available in the United Kingdom since November 2021. More details:

Stokes Pharmacy is a privately owned compounding pharmacy that formulates custom prescription medicines for humans and animals. It has been in business since the mid-1970s, evolving from a small hometown operation in Medford, New Jersey, to a respected pharmacy serving the entire United States, enabled by sophisticated online ordering and overnight shipping capabilities. Stokes has built a reputation for unwavering quality and superb service and has always put safety and quality first.

Stokes Pharmacy aims to ensure that every compounded medication that leaves its facility is formulated precisely as prescribed. They use only raw materials (purchased from reputable providers) that meet the United States Pharmacopeia (USP) standards and routinely monitor their laboratory and cleanroom environment to maintain integrity and control of their facility.

FIP treatment US - Stoke GS pillsTheir compounded 50 mg tuna-flavored quad-scored tablets (smaller than a U.S dime coin) are the ONLY oral formula identical to the Bova formula which has been utilized in clinical research studies worldwide and is currently in use in the U.K. and Australia. This U.S.-made compounded oral treatment for FIP was made available as of June 1, 2024, by a veterinarian prescription and for office use in permitted states.

The FDA (U.S. Food and Drug Administration) released an official announcement on May 10, 2024, addressing their position on the use of compounded GS-441524 to treat FIP.  Full details available

The FDA’s Center for Veterinary Medicine (CVM) has notified veterinarians that compounded GS-441524 falls under Guidance for Industry (GFI) #256 and is allowed to be compounded and legally prescribed. 

The availability of this compounded FIP treatment is a welcome development to the cat-loving public and veterinary professionals alike providing a major ray of hope in treating a previously considered almost always fatal disease. In addition, GS-441524 was nominated and is now on the GFI under review list for the animal drug bulk substances list regarding GFI #256 office use. This means that Stokes Pharmacy’s GS-441524 50 mg tablets can be sold to hospitals for office use in all states EXCEPT Arkansas, Maine, Massachusetts, New Mexico, New York, Oregon, Rhode Island, and West Virginia. Veterinarians who work in a state that does not allow USP compounded medications for office use can prescribe the drug in a patient’s name.




Please make sure to discuss with your veterinarian the cost of the treatment and also the shipping method (overnight is available upon request). Pricing information can be found on the Stokes Pharmacy’s website but does NOT include shipping (or tax when applicable). 

Each tablet can be quartered for multiple strengths and the cost of the full treatment will vary based on several factors including (but not limited to) weight changes during the treatment course. 

If you have pet insurance and would like to seek reimbursement for the Stokes Pharmacy’s GS-441524, please contact your insurance provider for more information. Well-known and leading pet insurance provider TRUPANION has already announced they are ready to increase access to lifesaving FIP medications to its customers. TRUPANION has been providing this coverage in other countries where the FIP treatments are commercially available and moving forward will play a role in the fight against FIP in the United States. 

More details are available in this Press Release/Business Wire article:

Treatment (or euthanasia) of cats with suspected FIP should ONLY be considered after EVERY effort has been made to obtain a diagnosis. A balance between the costs of diagnostic testing and treatment should be made, and veterinarians should be confident that FIP is the very likely diagnosis before starting a treatment with antivirals due to the cost and length of treatment required. It is worthwhile to note that drug resistance is relatively common for antiviral agents (especially with prolonged drug exposure). At this time, it is estimated that a very small percentage of cats (about 3%) are resistant to antivirals used to treat FIP. That being said, resistance is a real threat and has to be avoided. Meaning, that the use of antivirals should be strictly considered ONLY for the treatment of cats with FIP. It is HIGHLY recommended not to use antivirals in healthy FCoV-infected cats, given the potential for resistance to develop.


GC376: GC376 is a broad-spectrum anti-viral under development by Anivive Lifesciences for therapeutic uses in humans and animals. The California-based biopharmaceutical company licensed the exclusive worldwide patent rights to GC376 from Kansas State University. It is worthwhile to note that since 2020, GC376 is being investigated as a treatment for Covid-19. This anti-viral has shown activity against many humans and animal viruses including coronavirus and norovirus. The most extensive research has been in several in-vivo studies treating cats with FIP. Like all coronavirus, the FIP causal pathogen contains an enzyme responsible for the replication of the virus. GC376 (3C-like protease inhibitor) successfully halts the replication process. Learn more at:

INTERFERON / Virbagen Omega™ (Virbac): Interferons are a group of naturally occurring proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens. They are named for their ability to “interfere” with viral replication by protecting cells from virus infections. In other words, they are broad-spectrum antivirals that the body produces. They also may activate immune cells and increase host defenses. Since the action of interferon is species-specific, feline interferon is more efficacious than human interferon. 

Virbagen Omega™ (Virbac) works by stimulating the immune system to attack the virus. The active substance of Virbagen Omega is omega interferon and is produced by a method known as “recombinant technology”. Recombinant feline interferon omega (IFN omega) – was first used in the treatment of FIP by Japanese veterinarian and scientist Dr. Takou Ishida back in 2003. Virbagen Omega™ (Virbac) is available in many countries. More details can be found at:

A large number of cases of FIP in recovered cats have been documented in the field. Despite potentially good circumstantial evidence that is obtained from the cats’ parents, without viral genomic sequencing, it would be difficult to determine whether a further bout of FIP in a recovered cat is due to re-infection or recrudescence of the previous infection. The issue of re-infection and FIP (as opposed to treatment failure/relapse) currently isn’t well documented in scientific papers but it is safe to assume that this issue of recrudescence vs. “de novo” infection will be an active study area in the near future.

At the moment, there isn’t much to add about this. However, given that (a) new treatments such as GS-441524 act to directly inhibit viral replication, but will have no long-lasting protective effect and (b) that the antibody response in cats with FIP is strong (i.e: high titers) but ineffective (do not develop an effective immune response to infection), it would seem highly possible that re-infection could cause FIP. While many of the same risk factors may still be at play in a recovered cat (e.g. purebred status, multi-cat household, stress, etc.) the cat will inevitably be older which in itself helps reduce the risk of FIP. In the absence of proper data, it is sensible to recommend maintaining vigilance in recovered cats and, so far as possible, minimizing the risk factors associated with FIP and this includes avoiding (or at least limiting) exposure to FCoV and minimizing stress. 



POLYPRENYL IMMUNOSTIMULANT™, commonly refer as PI or PPI is the only veterinary biologic licensed by the U.S Department of Agriculture for symptomatic treatment of Feline Rhinotracheitis Virus (FVR) infection and it is safe in cats over 8 weeks of age. Previous studies by the research group, including the pilot study led by Alfred Legendre, DVM, MS, DACVIM (University of Tennessee College of Veterinary Medicine) back in 2006 indicated that the product might benefit cats with the dry form of FIP. PI boosts cell-mediated immunity and could theoretically be used to treat diseases in which cellular immunity is suppressed, like FIP.

Feline viral diseases develop when a virus is using the cat’s cells to replicate. The cat’s body protects itself with a system of defenses known as immunity and because it is this immunity that protects the cat then it becomes the first target of viruses, one way or another, the invader needs to break through the defenses. Polyprenyl Immunostimulant™ is manufactured by Sass & Sass, Inc and it is a very safe, well-tolerated oral liquid designed with only cats in mind. PI works to stimulate the body’s immune system to fight those formidable enemies called viruses.

In recent years with the introduction of newer antivirals to treat FIP, much emphasis has been placed on the role these novel drugs play. However, an important message has been ignored by many in the FIP field – simply put: antiviral drugs alone aren’t enough to effectively fight viral diseases.

The pathogenesis (development of a disease) of FIP is complicated: the reductionist view is that it is entirely due to the mutation of the virus. Whilst this internal mutation theory is the most widely accepted, no consistent mutation has been identified. The holistic approach is that FIP occurs as a result of several factors, including viral load, the immune status, and the general health of the cat. The one thing that is simple to understand is that FIP like most viral infections starts and ends with immunity.

Immunomodulatory medicines are new and designed to rebuild the damaged immunity and direct it against invading viruses. In other words, a medicine that stimulates immunity helps the body fight the disease and with a restored immunity the cat’s body can control or suppress the virus. Given these facts, it is clear that the best approach for an effective treatment for feline infectious peritonitis (FIP) is to combine an antiviral and an immune response modifier. Learn more at:

POLYPRENYL IMMUNOSTIMULANT ™ (PI – PPI) is available worldwide except in a small number of countries due to specific regulations or contractual limitations. More details about product availability and ordering processes are available at:


In situations where it is not possible to have access to any of the treatments mentioned above (or as palliative end-of-life care), veterinarians can prescribe medications that help bring relief from the symptoms experienced. Supportive care such as IV fluids, blood transfusions, and fluid drainage may be necessary to keep cats more comfortable. FIP treatment may also include corticosteroids, antibiotics, and cytotoxic medications. Prednisone (also known as Prednisolone) is a known synthetic corticosteroid and it was the main anti-inflammatory and immunosuppressant used to help cats with FIP. Prednisone is inexpensive and available everywhere.

It is worthwhile to note that cats require higher doses of prednisone, unlike other pets. Like most corticosteroid drugs, prednisone provides quick relief from symptoms of terminal illnesses making the cat feel better. It also stimulates appetite. Prednisone in low doses effectively soothes inflammatory conditions. High doses of corticosteroids are effective in pets suffering from immune system diseases and cancer.

Cats that are administered prednisone for over seven days become dependent on the medication. In addition, long-term use of prednisone disrupts the body’s normal adrenal functioning. As prednisone suppresses both the humoral and cell-mediated immune response, the doses MUST be reduced to a level that keeps the cat comfortable. Prednisone has several side effects that may be both short-term and long-term. Cats may experience excessive thirst and urination, fluid retention, intestinal disorders, and vomiting. The long-term side effects of prednisone include eye disorders and Cushing’s disease. Prednisone should never be used in cats with toxoplasmosis, or leishmaniasis, neither is safe in cases of septic peritonitis or pleurisy. We can’t emphasize enough that before treating the cat, every effort must be made to ensure a correct diagnosis.


Because the dry form of FIP progresses more slowly, cats with this form can sometimes live longer than those with the wet form. This is especially true if the eye is the only organ affected by granulomas. Cats who have an appetite, no neurological signs, and no anemia usually respond better to supportive care.

Supportive care includes: 

  • Periodic draining of abdominal or thoracic (chest) fluid in those with the wet form. Please note that if the fluid is drained too often, the cat loses large amounts of protein which can exacerbate the condition.
  • Fluid therapy
  • Quality nutrition
  • Antibiotics for secondary bacterial infections
  • Blood transfusions in cases of severe anemia
  • In cats with eye involvement, ophthalmic solutions containing corticosteroids, and injections of steroids into the inner side of the eyelid (conjunctival sac) can be used.



If the FIP case is presenting with elevated liver enzymes and/or if using a nucleoside analog drug that can be hepatoxic, drugs such as s-adenosylmethionine (SAMe), Silymarin (also called Milk Thistle), Denamarin, or Hepatosyl must be part of the treatment to protect the liver.


  • VITAMIN B12 (also called cobalamin): Vitamin B12 is crucial to the health of your cat’s immune system, nervous system, and digestive tract. It helps to stimulate appetite, supports red blood production, and also has anti-inflammatory properties. It is recommended not only for cats sick with FIP but also for cats who are FCoV infected and suffering from diarrhea.
  • VITAMIN B1 (Thiamine)
  • VITAMIN A (Antioxidant)
  • VITAMIN C (Antioxidant)
  • VITAMIN E (Antioxidant)
  • Metacam/Meloxicam (pain reliever)


  • Cerenia (by Rx only)
  • Slippery Elm Bark (supplement)


These meds should be administered if the cat is not nauseated or if nausea was previously addressed otherwise they can make things worse.

  • Mirataz (ear ointment)
  • Mirtazapine
  • Cyproheptadine (when Mirataz/Mirtazapine/Maropitant fail


A cat’s body needs a lot of nourishment during the treatment of FIP as there is so much for the body to repair. To recover, your sick cat needs to have both food and water. When cats are ill, they will often stop eating and drinking, therefore, it is important to monitor your cat’s food and water intake so that you know when intervention is necessary. It is important to separate your sick cat from other pets in the household so you know who is eating the food.

Fresh water should be available at all times. Healthy cats that eat canned food often drink very little because the food contains a high proportion of water. If your cat stops eating, then there is the need to have additional fluids. Fluids can be administered by mouth using a syringe. Your veterinarian will give you specific instructions on how much and how often to administer fluids. If it is not possible for your cat to be given fluids by mouth, your veterinarian will hospitalize your cat to provide the necessary supportive care.

Encourage your cat to eat small, frequent meals of palatable, high-energy, highly digestible food. Warming food to body temperature often makes it more appealing. Some sick cats can be encouraged to eat more by hand feeding. Your veterinarian will advise you if there are any foods that you should not offer. If your cat cannot be tempted to eat voluntarily, your veterinarian may suggest giving liquid food via a syringe. An alternative (last resource) is to hospitalize your cat to feed him/her via a feeding tube.

These are some foods that you should consider:

  • Hills A/D Diet (canned) – This is a high-protein food that can be syringed into the mouths of cats and kittens that refuse to eat on their own. It is highly palatable food and little water can be added to boost the cats’ fluid levels. It can be sourced at vet clinics or in some countries at pet stores via a prescription approval from your veterinarian.
  • Royal Canin Recovery Diet (canned) – This is quite similar to the Hills A/D and can be administered the same way. Available at veterinary clinics or in some countries at pet stores upon authorization from the treating veterinarian.

It is extremely important to remember that cats are obligate carnivores, and they developed unique strategies to utilize protein, fats, carbohydrates, and vitamins. While cats can metabolize carbohydrates, they are not an essential dietary nutrient for them. As a result, cats do require high-quality proteins in their daily diet. You may consider giving a tablespoon of real meat (preferably cooked) daily to augment arginine levels or use commercially available real meat-based cat foods. Highly processed, pro-inflammatory grain-based commercial foods should be avoided. Cats sick with FIP could be given small amounts of salmon, sardines, or other fish rich in omega-3.


The majority of a cat’s immunity resides in its digestive tract thus keeping it balanced with an array of good bacteria is a great way to ensure that your cat stays healthy. One possible way to do that is by supplementing your cat’s diet with probiotics – friendly bacteria that help to regulate digestive and overall health. These live microorganisms are believed to help treat or prevent a variety of illnesses and diseases, especially those related to the gastrointestinal system.

One might speculate that probiotics may adjust the microbiome for the better and that in turn may make the intestines a less hospitable place for a virus. There is a lot of work being done at the moment on the relationship between the gut microbiome and health and is considered very much to be a two-way process. Choosing a good quality probiotic may promote a healthier gut environment in terms of the microbiome and mucosal immunity, resulting in a hostile environment to the vile feline coronavirus.


When your cat is being treated, you must follow your veterinarian’s advice and instructions precisely. Take your cat for re-examination if and when requested. If your cat’s condition worsens unexpectedly, contact your veterinarian immediately for advice.

During its convalescence, your cat should be in a location that is warm, dry, peaceful, and quiet. There should be sufficient light for you to observe your sick cat. It may be necessary to provide an additional heat source such as a heating pad set on a low setting, a heat lamp, or a hot water bottle. These should be used with care to avoid burns or overheating. A litterbox should be provided within easy walking distance of your cat’s bed. It is often necessary to have a litterbox with low sides to make access easier for an ailing cat (especially for FIP cases presenting with neurological signs affecting mobility and balance). You may improvise a litterbox by cutting down the sides of a cardboard box, or by using a shallow baking pan and lining it with a plastic bag to contain the litter.

DISCLAIMER: The use of this website is at your own risk. This website is for information purposes ONLY, and it is NOT meant to replace a consultation with a fully qualified veterinary surgeon (veterinarian). It is NOT intended to be used to diagnose or treat any cat. The creators share their personal experiences, recommendations of treatments, foods, medications, supplements, and products for informative and educational purposes exclusively. The information in this site cannot and should not be used as a basis for diagnosis or choice of treatment. Creators and contributors exclude all liability whatsoever for any loss or damage arising out of use of this site or reliance upon its contents. Furthermore, creators and contributors strongly advise all users to always seek the advice of a qualified veterinarian and to obtain professional advice on the correct regimen for your cat and his or her particular situation. NO responsibility can be accepted.