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Note: this section is intended for veterinary surgeons only and should NOT be used by cat guardians to attempt to treat cats themselves. However, before leaving the page, guardians please download the following to take to your veterinary surgeons:

FIP diagnosis algorithm (this will open in a new window)

Questionnaires for step 1 of the FIP diagnosis algorithm for guardians to complete and give to your veterinarian to save time during your veterinary consultation

FIP treatment summary information sheet – vets, if you don’t want to go through all of this webpage, this sheet cuts to the chase in regards to dosages, etc.

Note - these downloads should open in a new window

When I first came to Feline Infectious Peritonitis research, FIP was regarded as an incurable condition. Most reported "recoveries" were probably curable conditions wrongly diagnosed as FIP. However, it is my belief that if diagnosed early enough, some cats with FIP can be cured. With the introduction of feline interferon we now see a glimmer of hope: treatment can occasionally effect a remission, sometimes for months and some cases recover completely. However, a lot more work requires to be done. The emphasis must still be on totally preventing cats ever developing FIP in the first place, and on accurate diagnosis, so that cats with non-FIP conditions are not needlessly euthanased.

This webpage represents only the personal opinions of the author, not all opinion leaders agree with me.

1. Double check the diagnosis

2. Nutrition


  • GC376
  • Virbagen Omega

4. CORTICOSTEROIDS / IMMUNOSUPPRESSANTS - given to both effusive and non-effusive FIP cases

5. EFFUSIVE FIP - treatment for cats with wet FIP

6. NON-EFFUSIVE FIP - treatment for cats with dry FIP


8. FCoV associated DIARRHOEA 




12. References and further reading


Before commencing treatment, make absolutely certain that the cat really does have FIP: around 80% of cases presented to me as FIP turn out to have some other condition. Work through the FIP diagnosis algorithm and be sure that the cat ticks most of the boxes of all of the steps. It is essential to ensure that the diagnosis is correct: immunosuppressive drugs will markedly worsen other conditions (such as bacterial peritonitis or pleurisy) and even be fatal in other cases, for example toxoplasmosis, leishmaniasis.

To see me working through FIP diagnosis algorithm on a real life case, watch "Does Pancho Have FIP?" (It will count for 15 minutes of Continuing Professional Development.) More cases will be uploaded to YouTube. Also see the FIP diagnosis webpages.

2. NUTRITION  - this section applies to cats with wet or dry FIP; FCoV associated diarrhoea and asymptomatic healthy FCoV infected cats

The beauty of altering nutrition immediately is that it will help in any condition, not just FIP – and it is safe.  If you have read The China Study, watched Forks Over Knives, or heard Dr Michael Greger’s famous top human killer diseases lecture, you will already be familiar with the enormous impact diet has on preventing, and even curing, most of the main reasons for human deaths - the situation in cats and dogs may well be similar.

It is my opinion that feeding as varied and natural a diet as possible to cats with FCoV infection and FIP is essential: avoiding highly processed, pro-inflammatory grain-based commercial foods (even the expensive so-called “veterinary” diets are usually cereal based). 

Unlike humans, arginine is an essential amino acid in the cat (Morris & Rogers, 1978): this is why they are obligate carnivores. Arginine is essential not only for the urea cycle but also for the normal functioning of monocytes and endothelial cells. To see an animation of feline coronavirus infecting a monocyte/macrophage, and wet FIP developing, visit:

Give real meat daily to augment arginine levels: even just a tablespoonful a day will make a difference to FCoV infected cats.  It is important that the meat or liver come from free range animals because they will have eaten grass which is rich in omega 3. Alternatively, regularly use commercially available real meat based cat foods e.g. Applaws (MPM products, available from the Zooplus website in Europe); Wild Kitty Cat Food. 

Feed cats with FIP a little salmon, sardines, pilchards or other fish rich in omega 3
Increase the anti-inflammatory omega 3 fatty acid content of the cat’s diet (i.e. add sardines, pilchards, salmon, mackerel twice a wk for 6 weeks). Both Applaws and Almo Nature have canned food including real fish. However remember the risk of hypervitaminosis A (excessive laying down of bone at the joints) so be wary of feeding too much real fish – reassess the situation after 6 weeks.

Cereal based foods contain too much omega 6 polyunsaturated fatty acids and too little omega 3, leading to a state of chronic inflammation – we have seen this in human beings over the past couple of decades: an unprecedented rise in inflammatory conditions such as allergies, asthma and arthritis.  We see a similar rise in inflammatory conditions being recognised in the cat.  

Remember to instruct the cat’s guardian in a gradual changeover of the food: to change it over a period of weeks otherwise the cat will wolf down the new food for a few days, then get sick of it and never touch it again!  The way to introduce a new food is to give it for one meal, then go back to the customary diet for the next few meals, then give a little of the new food again, and so on, gradually increasing the frequency of the new foods, until giving a different food every meal becomes the norm for the cat.  To introduce new foods gradually properly will take at least a month.  

FCoV associated diarrhoea helped by chicken and pumpkin cat food
I’ve had remarkable success using Applaws or Almo Nature chicken and pumpkin tinned food in these cases.

You can get a discount on these cat foods at Zooplus by following this link:




GC376 is a 3C-like protease inhibitor antiviral drug, not currently commercially available. In the most recent field trial, 7 of 20 cats experienced remission. Here is a figure from the publication by Prof Pedersen et al:


Updates on this experimental drug can be found at








Because FIP is an immune mediated disease, therapy includes suppressing the immune response, usually with corticosteroids. Anti-viral treatments alone don't usually prolong the cat's life by much and many are quite toxic to cats. It is also important to maintain the cat's general nutrition status, by adding vitamins and antioxidants. Before embarking on any of the following therapies, it is essential to ensure that the diagnosis is correct, immunosuppressive drugs could markedly worsen other conditions (such as bacterial peritonitis or pleurisy). See Diagnosis of FIP

I should very much like to conduct a clinical trial on the effectiveness of various treatments for FIP, but unfortunately don't have the funding to do so. I'd like to thank Mr Wayne Carr and all the other donors to the Angelica FIP trust, whose generous donations made some preliminary investigations possible.

Vitamins and antioxidants
Other supportive drugs
Thromboxane synthetase inhibitors
Monitoring treatment / Prognosis
Further reading



Cats receiving immunosuppressants should also receive antibiotic cover to protect them against other infections.



Prednisolone is the main immunosuppressant used in feline infectious peritonitis, it is safe, tends to make the cat feel better and stimulates his or her appetite. I treated one cat with dry FIP with prednisolone alone and he survived for 10 months. Prednisolone suppresses both the humoral and cell-mediated immune response.

Prednisolone has the advantage of also being the treatment for lymphocytic cholangitis, which can be mistaken for FIP, so where the diagnosis is in doubt, prednisolone can be given anyway: the cat with lymphocytic cholangitis has a good chance of recovery, the cat with FIP unfortunately will die.

Prednisolone should never be used in cats with septic peritonitis or pleurisy, which is why cytology is a very important part of FIP diagnosis, as there will be many more white blood cells in the effusion of a cat with sepsis, and a good cytologist will detect the bacteria or fungi.

Dose: 2-4mg/kg/day given by mouth, sliding dose every 10-14 days, until optimal dose for that cat is found.


The rationale of using thalidomide in the treatment of feline infectious peritonitis is to reduce inflammation and the humoral immune response to feline coronavirus while leaving the cell mediated (anti-viral) immune response intact. Only 4 cats with FIP have been treated with thalidomide so far and unfortunately all died. However, one with a thoracic effusion did eliminate his effusion and had a remission of 3 months. I think that, to be effective, thalidomide would need to be used very early in the disease, before too many blood vessels became damaged.

Be sure to obtain the owner's consent for using a drug not licenced for cats.

Dose: 50-100mg at night. CANNOT BE USED IN PREGNANT CATS as it is teratogenic.



Feline interferon omega

Human interferon alpha

Feline interferon omega
Virbagen Omega (made by Virbac) is recombinant feline interferon omega (IFN omega) is available in many countries now. This product was first used in treatment of FIP by Japanese vet and scientist Takuo Ishida. This is his protocol:
IFN omega was initially given subcutaneously at 1 MU/kg every other day, and then once every week for variable period if remission was seen.

Glucocorticoid: (dexamethasone 1 mg/kg intrathoracic or intraperitoneal injection once only) or prednisolone. Oral prednisolone was initially given at 2 mg/kg once daily, and the dosage was gradually tapered to 0.5 mg/kg every other day after remission.
In Dr Ishida's study, 4 cats of 12 completely recovered and two survived 4 and 5 months. Those cats which recovered completely all had the effusive form of FIP and were relatively older cats.

I am working alongside vets in practice in the UK to monitor a number of cats being treated with this product. It seems to be very important to begin treatment as soon as possible after the onset of clinical signs. We are seeing success in younger cats too, and even cats with non-effusive FIP. Some cats are being treated orally using 100,000 Units a day. Once diluted (in water or saline) IFN Omega maintains its potency in the fridge for up to 3 weeks, so keep most IFN Omega in the freezer until needed.

Diluting feline interferon
Virbagen Omega comes in vials of 10 million units. It is reconstituted with 1ml of diluent. To get 100,000 Units/ml, divide one vial into 10 x 0.1ml aliquots in 10 one ml syringes and freeze 9 of them. Put 4.9mls of saline or water into a small clean tube and add one of the 0.1mls of Virbagen Omega to it: you now have 5 mls of diluted interferon: store it in the fridge (where it will keep up to 3 weeks). Show the cat's guardian how to withdraw 0.5mls of the diluted interferon (which now has 100,000 units of interferon per dose). Get the cat's guardian to do the syringe filling and the dosing in front of you: we vets are so used to handling syringes that we forget that most people have never handled a syringe in their lives. Some cats will take the interferon on food, but to be certain the cat gets the dose, tilt the head with the mouth closed and introduce into the commisure of the lips, wait until you see the cat swallow before releasing the head.

Remember that reconstituted, diluted Virbagen Omega lasts only up to 3 weeks in the fridge.

Updates on treatment will appear in the English version of the website before the translated pages.

Suppliers: Virbagen Omega can be obtained from your Virbac representative. From abroad, it can be bought at Abbeyvet, who can be contacted at

In the USA, Virbagen Omega is stocked by The Animal Medical Centre, 510 East 62nd Street, New York, NY 10065. Telephone: (212)-329-8724

Reference: Ishida et al, 2004. Journal of Feline Medicine and Surgery. Vol 6 Issue 2 pp 107-110

Human interferon alpha
Dose: Non-effusive feline infectious peritonitis (FIP): 30 i.u./daily or for 7 days at alternate weeks given by mouth.

In effusive FIP 30 i.u./daily can be used, or larger doses of interferon can be given by intramuscular injection daily (104 - 106 i.u. per day). By 6-7 weeks, if the cat is still alive, interferon will no longer work at this dose because the cat will make antibodies against it.

To obtain human interferon-alpha (Roferon or Intron A), write a prescription for your local pharmacist. Obviously, in areas where feline interferon is available it is preferable as it is likely to have more effect than the human interferon.

Diluting human interferon
To get 30 i.u./ml: Intron A can be obtained as 1 million i.u. for about 10.00. Dilute whole vial in one litre of saline, giving 3000 i.u./ml. Put one ml of 3000 i.u./ml into 99ml of saline, to get 30 i.u. per millilitre. Aliquot into 1ml volumes* and freeze for up to a year. Defrost as required, keep refrigerated for up to a week.

*In the UK: 2ml tubes are available from Sarstedt, supplier's ref: 72.694.006. Fax: 0116 236 66099 Tel: 0116 235 9023.

To get 104 i.u./ml put 1 x 1 million i.u. vial of Intron A or Roferon into 99ml sterile saline and divide into 1ml doses and freeze. For 105 i.u./ml use 9mls saline and proceed as above. For 106 i.u./ml use the whole vial.



Vitamins and antioxidants

Vitamin A
Vitamin A is an antioxidant. The dose of Vitamin A is 200 i.u./day given by mouth or in the food. Cats cannot metabolise the beta-carotene form so must be given vitamin A as fish oil, e.g. halibut liver oil. Too much vitamin A can cause excessive laying down of bone at the joints, so don't use this supplement for more than 4-6 weeks.

Vitamin B1 (thiamine)
Vitamin B1 (thiamine): 100 ug/day given orally (i.e. by mouth or in food).

Vitamin B complex

Multivitamins B are a good appetite stimulant and can be obtained from health food shops or chemists (I particularly like the one from Boots). Dose: paediatric dose.

Vitamin C
Ascorbic acid 125 mg twice daily given by mouth or in food. Vitamin C is an antioxidant. Remember that given over a long period of time, vitamin C can predispose to oxalate crystals in the urine.

Vitamin E

Dose of vitamin E: 25-75 i.u./cat twice dailty given by mouth or in food. Vitamin E is an antioxidant.

Other supportive drugs

For anti-inflammatory activity and pain relief.

Dose: 10mg/kg every 48-72 hrs per os.

Antibiotic cover is essential when immunosuppressing a cat.

Dose: 50 mg bid per os.

Anabolic steroids
For appetite encouragement and anti-catabolism, especially if the kidneys are affected.

Choose from the following (in the UK):
Laurabolin injection: 2-5mg/kg every 21 days.
Nandrolin injection: 2-5mg/kg as a weekly injection.
Nandoral tablets - one a day either whole or crushed into food.
Retarbolin injection: 1mg/kg every 21 days.
Orandrone tablets: 0.5mg/kg daily (the tablets are 5mg).

Remember to warn the owner that the cat's urine could become more strong smelling with this treatment.
The injectables usually require to be kept in the dark.

Probiotics such as Protexin Pro-Kolin+  can help cats with FCoV associated diarrhoea.

Thromboxane Synthetase Inhibitors

Two cats with abdominal effusions were treated with ozagrel hydrochloride with success (Watari et al, 1998).

Dose: 5-10mg/kg twice daily and prednisolone at 2mg/kg/day.



Whatever treatment you opt for, it is important to monitor the cat's progress. Initially, I measure the haematocrit (Hct), globulins, albumin to globulin ratio (A:G), alpha1-acid glycoprotein (AGP) and the cat's weight every 7-14 days to see how the cat is progressing. Later
, examinations might only be monthly if the cat is doing well. It is not worth measuring the FCoV antibody titre more often than every 2-3 months, there will be no discernible difference within a shorter period. The AGP should be the first to fall if treatment is having a positive effect because AGP is a measure of inflammation. Positive signs are globulin levels decreasing, and the albumin: globulin ratio(A:G) increasing, Hct increasing and reticulocytes appearing in blood smears and weight increasing. Negative signs are AGP remaining high, globulins staying high or increasing, A:G decreasing, weight loss. When Hct gets to below 20% and is non-regenerative (no reticulocytes seen on blood smear examination) then the cat should probably be humanely euthanased if your clinical opinion is that he or she is no longer getting any happiness out of life. Clearly, if the cat is distressed at any point in the treatment, then euthanasia will be required. Sadly, cats with effusive feline infectious peritonitis usually only survive a few days, possibly weeks at best. Cats with non-effusive FIP can last many weeks or months, though after neurological signs begin euthanasia usually ensues fairly rapidly.

For AGP testing see Companion Animal Diagnostics.

Further reading

""Feline Infectious Peritonitis and Coronavirus" - download an ebook written for cat guardians or purchase the physical version from Amazon.

This book is written for anybody unfortunate enough to have had FIP diagnosed in their cat. It will help you through the maze that is FIP diagnosis, to decide what your options are for treatment and to safeguard your other cats, or how and when to safely add a new cat to your household.

Please note that this is a zip folder containing an .exe file and that you may have to alter your firewall or virus protection program to allow it to download. This is a new experiment for us, so please let us know if you encounter any problems downloading it (email e-books @ You can still use the regular Buy Now buttons below to purchase the e-book if you prefer.

At present, you can only buy the whole eBook directly (and within minutes) from the sample eBook in US dollars. To buy it in GB pounds or Euros, please use the Paypal links below and we will manually send you an activation key within 24 hours. A physical version can be obtained from any of the Amazon websites.

Note that everything in these books is available for free here on the website!


The chapters are:

1. Everything you need to know when your cat has been diagnosed with FIP

...... Download FIP diagnosis Step 1 questionnaires to take with you to your veterinary surgeon

........(This download will open up in a new page as a word document.)

2. Everything you need to know about treating a cat with FIP

...... Download a current FIP treatment sheet from the Downloads menu to take with you to your veterinary surgeon.

3. Preventing your other cats or kittens from developing FIP

4. Everything you need to know about getting another cat or kitten

5. Everything you need to know if your cat or kitten is diagnosed as having diarrhoea caused by FCoV

6. Everything you need to know if you work in a rescue shelter or boarding cattery

7. FCoV/FIP prevention in trap, neuter, return (TNR) programs

8. Everything you need to know if you keep a lot (over 6) pet cats, or have a cat sanctuary or colony

9. Everything you need to know if you are a cat breeder

10. What you can do to help fight FIP

11. Everything you need to know to find more information

Download the photographs from the book in colour (this will open as a .pps in a new window).

To buy in UK pounds
£5.00 GBP:


To buy in US dollars


To buy in Euros
€7.50 EUR:



12. References and further reading

Addie D.D., 2004 Feline Infectious Peritonitis. Veterinary Interferon Handbook. Ed: Karine de Mari. Virbac. 108-117

Addie D.D 2008  Feline Infectious Peritonitis   Veterinary Interferon Handbook 2nd edition.  Ed. K. de Mari. Virbac SA, BP 27, O6510 CARROS, France. 132 - 146

Addie D.D.2008  Feline infectious peritonitis – therapy and prevention.  Kirk’s Current Veterinary Therapy XIV Edited by: John D. Bonagura, DVM, MS, DACVIM, David C. Twedt, DVM, DACVIM. Saunders, Elsevier.1295 – 1299

Addie, D.D.. Feline coronavirus. 2012  Infectious Diseases of the Dog and Cat.  4th edition.  Editor: Greene, Craig. Published by W.B. Saunders Elsevier Company, 11830 Westline Industrial Drive, St. Louis, Missouri 63146, USA. ISBN 978-1-4160-6130-4   92-108

Gunn-Moore D, McCann T.  2004 Use of recombinant feline interferon to treat feline infectious peritonitis.  Veterinary Interferon Handbook. Ed. Karine de Mari. Virbac  118-124

Hartmann K, Ritz S.  2008 Treatment of cats with feline infectious peritonitis.  Vet Immunol Immunopathol.  123(1-2):172-5.

Ibarrola P, Blackwood L, Graham PA, Evans H, German AJ.  2005 Hypocobalaminaemia is uncommon in cats in the United Kingdom. J Feline Med Surg. 7(6):341-8.

Ishida T, Shibanai A, Tanaka S, Uchida K, Mochizuki M. 2004 Use of recombinant feline interferon and glucocorticoid in the treatment of feline infectious peritonitis. JFMS 6 107-110

Legendre AM, Bartges JW. 2009  Effect of Polyprenyl Immunostimulant on the survival times of three cats with the dry form of feline infectious peritonitis.  J Feline Med Surg. 11 624-626

Legendre AM. 2013 Polyprenyl Immunostimulant presentation to AAHA abstract

Legendre AM, Kuritz T, Galyon G, Baylor VM, Heidel RE. 2017 Polyprenyl Immunostimulant Treatment of Cats with Presumptive Non-Effusive Feline Infectious Peritonitis In a Field Study.  Front Vet Sci. 4:7. doi: 10.3389/fvets.2017.00007

Maunder CL, Day MJ, Hibbert A, Steiner JM, Suchodolski JS, Hall EJ.  2012
Serum cobalamin concentrations in cats with gastrointestinal signs: correlation with histopathological findings and duration of clinical signs. J Feline Med Surg. 14(10):686-93.

Morris JG, Rogers QR.  1978  Arginine: an essential amino acid for the cat.  J Nutr. 108(12):1944-53.

O'Brien, DP & Packer, RA (2010) Metabolic encephalopathy: organic acidurias. In August, JR (Ed): Consultations in feline internal medicine. Vol 6. Elsevier Saunders, Philadelphia. pp:595

Pedersen NC, Kim Y, Liu H, Galasiti Kankanamalage AC, Eckstrand C, Groutas WC, Bannasch M, Meadows JM, Chang KO. Efficacy of a 3C-like protease inhibitor in treating various forms of acquired feline infectious peritonitis. J Feline Med Surg. 2017 Sep 1:1098612X17729626.

Reed N, Gunn-Moore D, Simpson K. 2007 Cobalamin, folate and inorganic phosphate abnormalities in ill cats. J Feline Med Surg.  9(4):278-88.

Ritz S, Egberink H, Hartmann K.  2007  Effect of feline interferon-omega on the survival time and quality of life of cats with feline infectious peritonitis.  J Vet Intern Med. 21(6):1193-7.

Simpson KW, John Fyfe, Angelyn Cornetta, Amy Sachs, Dalit Strauss-Ayali, Stephen V. Lamb, Thomas J. Reimers 2001 Subnormal Concentrations of Serum Cobalamin (Vitamin B12) in Cats with Gastrointestinal Disease  J Vet Intern Med  15:26–32

Tsai HY, Chueh LL, Lin CN, Su BL. 2011 Clinicopathological findings and disease staging of feline infectious peritonitis: 51 cases from 2003 to 2009 in Taiwan.  J Feline Med Surg.  13(2):74-80.

Watari T, Kaneshima T, Tsujimoto H, Ono K, Hasegawa A. 1998 Effect of thromboxane synthetase inhibitor on feline infectious peritonitis in cats. J Vet Med Sci. 60(5):657-9.

Weiss Richard C. 1994 Feline Infectious Peritonitis Virus: Advances in Therapy and Control in Consultations in Feline Internal Medicine 2. Edited by John R. August. Published by W.B. Saunders Company. Harcourt Brace Jovanovich, Inc., The Curtis Center, Independence Square West, Philadelphia, PA 19106. pages 3-12
ISBN 0-7216-4674-3




Dr Diane D. Addie 19 January 2018


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