New Treatments For FIP In Cats

“As of July 2019, over 2000 cats all over the world have been completely cured using the GS441 from China.” That’s the statement found on a website dedicated to a new drug for FIP in cats.

Why does it matter? Feline infectious peritonitis or FIP is probably the number one fatal viral disease of young cats around the world. Up to now FIP has had no effective treatments and no vaccine.

This is a note of caution to the tremendous excitement. I’m not saying it’s all fake or you shouldn’t use it, I’m just saying be careful. I’ll tell you why in a minute.

What Is FIP In Cats?

Feline infectious peritonitis is caused by a coronavirus that usually only causes diarrhoea. Many cats carry coronavirus and all they might experience is mild persistent loose stools.

There is no risk from cats to people. Feline coronavirus is completely separate from the human strains such as COVID-19

Cats don’t catch FIP, they develop it. FIP occurs when that enteric coronavirus undergoes mutation into the FIP strain inside the infected cat. However, virtually all coronavirus-positive cats never progress to developing FIP. It’s a rare and tragic accident when it happens.

FIP is more common in purebred and shelter kittens. I first saw it in UK where cats are often bought from shelters, and here in Australia I only see it in purebreds. It’s more common in these places because the cats are at a higher concentration, and enteric coronavirus infects the premises.

Probably all the cats in contaminated premises catch coronavirus, most shake it off, a few become carriers and a small number get FIP. That’s no comfort if it’s one of your cats that’s affected. FIP is estimated to cause the death of between 0.3 and 1.3% of cats worldwide.

Signs Of FIP In Cats

FIP comes in two forms, based on how the immune system responds. The wet form is caused by the laccumulation of large quantities of fluid in the abdomen and sometimes the chest.

This is often a very young kitten with a swollen belly or trouble breathing. The wet form is rapidly progressive and usually requires almost immediate euthanasia.

The dry form is much slower. The body’s response to the FIP virus produces solid tumour-like granulomas around the body, notably in the central nervous system and kidneys. Therefore, FIP is the great pretender. The symptoms will depend on the organ affected, and can be almost anything.

I have seen the dry form of FIP as either slowly growing lumps caused by enlarged lymph nodes or unexplained neurological disease. This could start as an unsteady gait, different sized pupils or a head tilt. These cats usually worsen steadily and waste away in the most horrible way.

There is nothing worse than watching your young kitten die a slow and relentless death. Up to now, there’s been little we could do about it. This gap has created desperate cat owners, ready to try anything, sometimes at almost any price.

In my opinion, not everyone who’s filled that gap has done so ethically.

Treatment Of FIP

Traditional treatment of FIP has been supportive, using good nutrition, anti-inflammatories and attention to secondary infections. However, the most important treatment has been timely euthanasia.

The problem with deciding to euthanase is that it’s nearly impossible to ever be 100% certain of the dry form. There is no test for FIP, and so the diagnosis is about building up a case, piece by piece. No one wants to end a life incorrectly, so these kittens often go on for some time.

I recently referred an affected kitten to specialists, and even they took nearly six months to be sure. This difficulty with diagnosis is extremely relevant in discussing the new treatments, as you’ll see.

Interferon For FIP

Interferon-omega is an injection marketed for cats with FIP. A small early study showed promising results and so for a brief period it became part of the standard treatment. However, that study was plagued by the faults of most early FIP papers.

A larger double-blinded placebo-controlled study found no benefit to interferon. That should have been the end of the matter, but the drug is still available, and people still push the earlier paper without reference to the later one. Like all these drugs, Interferon-omega is expensive.

Polyprenyl Immunostimulant

This is the one that frustrates me. If you read the reports, polyprenyl immunostimulant is a wonder drug. If you read the science with a vet’s eye, it all falls apart. These people almost certainly mean well, but they look a lot like people taking advantage of a bad situation.

The studies they quote lack control groups, have fatal flaws and make very unsound conclusions. It takes a whole webpage just to unpack the deficiencies of this product and its ‘evidence’. Is it any surprise that this is also an expensive drug?

GS-441524 and GC-376

GS441524 and GC376 are the two new antiviral drugs responsible for all the recent excitement. And to be fair, they show the greatest promise. Most of the attention has focused on GS441 as it’s often called.

A preliminary paper published last year showed encouraging results in a small study. Perhaps more important than the study itself was that it was in a prestigious journal by a respected author.

But there’s a problem: GS-441 is owned by a human pharmaceutical company whose main focus is developing an antiviral drug for Ebola. They have allowed this pilot study, and then stopped access to the drug while they focus elsewhere. This has encouraged the illegal production and sale of GS-441 from China.

GC-376, by contrast, is owned by a veterinary company, but still needs FDA approval to be released. This could be up to 5 years away.

A Note Of Caution

25 years of experience with miracle FIP treatments makes me naturally skeptical about new drugs. That doesn’t mean that they don’t work, but there’s good reason for being cautious.

It’s still too early to talk of a ‘cure for FIP’. The reason is that the evidence contained in the only paper published so far isn’t strong enough. Here’s why:

  • The paper only studied a small number of cases (31 cats)
  • There was no control group to compare the treatment against placebo
  • The study population was biased by excluding ocular and neurological cases*

* Exclusion was done because of concern over the ability of the drug to reach these areas. After this, only five remained with the classic dry form.

Let’s not forget that Interferon-omega was everyone’s greatest hope until a double-blinded and placebo-controlled study showed otherwise. Pedersen’s paper should be seen as no more than a feasibility study, but instead it’s being taken as proof of efficacy. It’s not.

To anyone reading the compelling stories of improvement during the treatment phase, this must sound like wilful denialism. Maybe it is. I actually think that GS-441 is the best chance we’ve had so far, especially for the wet form. But if we don’t adhere to the scientific method we risk ending up with thalidomide again*.

What To Do If Your Cat Has FIP

I will never criticise anyone who sources and uses GS-441. In fact, I’m not sure I wouldn’t do the same. FIP is terrible, and even a faint hope is sometimes worth grasping.

I have read the testimonials from cat owners convinced that GS-441 has saved their cat. They sound convincing, and may be true. However, when reading them my vet mind comes up with three things:

  1. We can rarely be certain of the diagnosis in a live patient and at least some of these cats never had FIP
  2. Survival times for the dry form of FIP go from days right up to several years without treatment
  3. Owners of cats who died quickly are unlikely to post their side of the story, even if it’s a lot more common

If you want to use GS-441, the problem isn’t in getting it, it’s using it. There are Facebook pages and websites devoted to assisting you (one is mentioned below in the comments), and while they can help you source the medicine, they aren’t vets.

By all means read what they say, but ask your vet for advice on safe dosing. We probably can’t legally buy the drug, but if you sign a disclaimer absolving us of blame, we are happy to help you use it as safely as possible.

Cost is also a barrier to many owners. We hear reports of the cost for a course of GS441 from $US2300 up to $10,000 depending on the supplier.

In reading owner reports, drug safety doesn’t appear to be a major problem, even with the knock-off GS441 from China. However, there’s no way of guaranteeing it will be as pure or as effective. Buying an unlicensed drug from such origins will always be riskier.

That’s just one of the prices we pay for caring so much. Sometimes it feels worse to be given a choice when it’s as imperfect as this one. We can only hope a registered drug fills the void soon, and with the evidence to match.

Further Reading

* I’ve been waiting years to ask you to read the story of Frances Oldham Kelsey. You won’t regret it. The world finds heroes in the most unlikely places.

Pedersen, N. C., Perron, M., Bannasch, M., Montgomery, E., Murakami, E., Liepnieks, M., & Liu, H. (2019). Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. Journal of feline medicine and surgery21(4), 271-281. Full text

By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on email and TwitterSubscribe via email here to never miss a story!
Have something to add? Comments are welcome below and will appear within 24 hours of lodging.


7 Replies to “New Treatments For FIP In Cats”

  1. I appreciate your insight on this disease and cures. I am part of a group of pioneers and warriors that are fighting FIP with gs441.
    We are 5000 strong as of today and there are more cats surviving on this than passing. Yes there are some that pass due to how weak the cat was before getting the medication. There are three types available now. One is a pill form and it is doing great also. Good for those who are not comfortable with giving injections. The source of the medication is reliable and it seems to be a saving grace for many!! My cat included. She is on day 24 of injections and she has completely turned around from wasting away and feverish and hardly moving, now back to her playful energetic and bright eyed self. There are many many more as well in this group of 5000 plus. Many of them are post treatment as far as 87 days post and completely turned around with perfect blood work and living a happy cat life. Many people are thankful for the opportunity to save their cat’s life. I wouldn’t just get the medication from anyone or any other source. The group I am in is a reliable source with many Veterinarians on board to look at bloodwork and offer suggestions for support. The entire group is like a family and we support each other and answer questions. Everyone is in various stages of the medication protocol. Everyone shares their ups and downs. New people are finding the group and joining daily! This is the FB group . I only know of one. It is a legitimate source for help. Lots of love and support here. Thank you for your article. I just wanted you to know that we are pioneering our way through this so far the outcomes are positive. We need to educate more veterinarians about this. I changed vets because my former vet scolded me and made me feel bad for seeking out a source to Save my cat rather than watch her die. I read lots of the same stories on my group page. Too many vets are uneducated about the medication and treatment. They make comments like it’s a bad thing or idea. Well what’s worse than watching your beloved cat die!??!! Trying the treatment is the best thing ever!! Because they are dying anyhow!!!!
    Why not try something that just might give them a chance.
    This group is better than any clinical trial because we are living proof that this works and we can follow up and see how it goes through the years.
    Bless any and all that are going through the ravages of this horrible disease. So far I am happy and my cat is doing great and I do not regret my decision to go forward with the medication.
    My new vet is on board with me and they are documenting my progress through this with excitement about the medication and how it’s working.
    Go Warriors!!! And Pioneers!!!!!!

    1. Hi. This sounds encouraging. How can I find more information on tor group? My cat is 2 years old and seems to be in early stages of fip.

      1. The Facebook page referred to by Jaci is called FIP warriors. They will give you advice, but I’m sure they will also strongly recommend you do it with a vet who is comfortable working with the drugs.

  2. Thank you for your balanced and informed perspective on what is a scary and emotive subject for cat owners, especially those like myself with young cats who actively suffer from corona virus flare ups.

  3. Thank you for your article, which I read with considerable interest.
    I have an 8-mths-old foster kitten who’s been diagnosed with dry FIP, after several consultations with our vet and a blood test.
    There is clear evidence of both ocular and neurological damage from this evil disease and he runs a high fever frequently. His appetite has diminished lately as well. It’s a truly heartbreaking experience and unfortunately, this very sweet, loving little boy is not responding favourably to Interferon. He is still being treated with anti-inflammatories and now also eye drops in his right eye, which started to show signs of following the course of his now-blind left eye…the one bright light in all this is that so far, the visible damage to this eye appears static and he can still see me.
    For various logical reasons, other infections were discounted by our vet and from my own research on this subject, I’m inclined to agree with her diagnosis.
    Although I’m no scientist or medic of any kind, I don’t believe that FIP is as rare as you might think, (as I’ve seen quite a few more cases of it among various shelter cats, and of varying ages but more often among kittens), and I can only hope that a reliable treatment (cure!) can be found and offered to us ASAP!
    Kind regards..

    1. Hi Suzanne. I think you are right in saying that FIP can be more common. It seems to vary depending on the prevalence, use and possibly also type of shelters. Here in Adelaide, FIP is quite rare and in fact I’ve not seen it in a moggy (tabby cat) for over 20 years. On the other hand, it appears to be increasingly common in purebreds. I’ve added worldwide prevalence data above to support your comment.

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