Feline infectious peritonitis (FIP): the complete treatment guide.
For years FIP was considered a disease without a way out. That is no longer the case: with antiviral treatment, most cats that complete the 84-day protocol reach sustained remission. Here is how to recognise it, how it is diagnosed, what GS-441524 treatment involves, and what happens afterwards. We ship across the Gulf.
From diagnosis to remission, in four parts.
Everything worth knowing about feline infectious peritonitis and its antiviral treatment, in the order you need it.
- 1
Recognise the signs
The wet form, the dry form, and what changes when there is ocular or neurological involvement.
- 2
Confirm the diagnosis
No single test confirms it: the answer comes from combining several with the clinical picture.
- 3
Start treatment
The 84-day GS-441524 protocol, and when injectable or capsule is the right route.
- 4
Through to remission
What to expect in the first weeks, the 12-week observation period, and relapses.
What feline infectious peritonitis is
FIP develops when feline coronavirus (FCoV) mutates inside the cat's body. Feline coronavirus itself is very common: most cats carry it without becoming ill. In a minority of cases it mutates into the FIP virus, which triggers an intense inflammatory response against the blood vessels and organs.
- 1
Wet (effusive) FIP
Fluid accumulates in the abdomen or chest. The cat looks swollen or struggles to breathe, and the case moves relatively quickly. That fluid can be assessed with a Rivalta test.
- 2
Dry (non-effusive) FIP
There is no significant fluid, but inflammatory lesions form in the organs. It affects the brain, eyes, kidneys or liver. It progresses more slowly but is harder to diagnose.
FIP itself does not pass from cat to cat.What moves between cats is feline coronavirus, through shared litter trays and bowls and through grooming. The mutation that causes FIP happens inside each individual cat, unpredictably. It is not the result of anything you did wrong at home.
Signs of FIP
Early signs are non-specific and easily confused with other illnesses. If any of these persist, it is worth getting advice.
- 1Fever unresponsive to antibiotics
- 2Loss of appetite and weight
- 3Lethargy
- 4Dull, unkempt coat
- 5Swollen abdomen
- 6Laboured breathing
- 7Eye inflammation or uneven pupils
- 8Wobbliness or seizures
- 9Jaundice
- 10Behaviour changes
Purring does not mean everything is fine.Cats with FIP often purr and appear settled even when seriously unwell. Cats also purr when frightened or in pain. What helps is recording the objective things each week: weight, appetite, litter tray use and behaviour.
How it is diagnosed
There is no single test that confirms FIP. The diagnosis comes from combining several results with what is seen in the consultation.
- 1
FCoV serology
Measures antibodies to feline coronavirus. Because so many cats have them, it confirms nothing on its own, but it contributes to the picture.
- 2
Rivalta test
Used where there is abdominal or chest fluid, it helps indicate whether that effusion is consistent with FIP. Quick and inexpensive.
- 3
Blood work
Assesses inflammation, immune status, and liver and kidney function. FIP tends to produce characteristic patterns that weigh heavily in the diagnosis.
- 4
Ultrasound
Detects fluid, enlarged lymph nodes and organ changes. It also helps locate the lesions of the dry form.
Time matters.FIP is progressive and the prognosis without treatment is very poor. Cats that start earlier do considerably better. While you wait for results, it is worth preparing for treatment in parallel with your veterinarian.
The treatment
GS-441524 is the most widely used antiviral treatment for feline infectious peritonitis today. It blocks coronavirus replication, and multiple clinical reports show high rates of improvement.
GS-441524, the 84-day protocol
Treatment runs 84 days, about 12 weeks. Stopping early raises the risk of relapse, so the course is completed even where signs resolved much sooner. The dose is set by the cat's weight and the form of FIP.
- Given every day at the same time, without skipping doses.
- With periodic blood work to track inflammation and organ status.
- After the 84 days, a 12-week observation period begins with no medication.
- 1
GS-441524 injectable
The route with the strongest clinical support. It works across all forms of FIP and allows precise, consistent dosing. In neurological and ocular cases, starting here is recommended.
- 2
GS-441524 capsules
For mild to moderate cases, they allow treatment without daily injections. Simpler to give and therefore easier to sustain across 84 days.
- 3
EIDD-1931 capsules
The active metabolite of molnupiravir. Considered as an alternative where GS-441524 has not given the expected response, in relapses, or in refractory cases.
With neurological or ocular signs, do not start with capsules.Those forms need higher concentrations of the antiviral. Treatment starts with injectables and does not move to capsules until neurological signs have resolved completely. Send us the diagnosis and the blood work and we will help match the protocol.
What to expect after starting
Most cats show changes fairly early, though the pace of recovery varies between individuals.
- FIRST DAYS
Fever falls
The first thing to shift. Appetite usually starts returning at the same point.
- FIRST WEEK
Energy returns
Many owners notice the change within the first seven days.
- TWO WEEKS
Fluid reduces
The abdomen settles, breathing eases and weight begins to climb.
- 84 DAYS + 12 WEEKS
Sustained remission
If no signs of relapse appear during the observation period, it is considered sustained remission.
Improving quickly is not a reason to stop.It is common for a cat to look unrecognisably well within days. The virus is still present. Completing the 84 days is what matters most in avoiding a relapse.
What goes alongside the antiviral
Treatment is not only the medicine. Day-to-day care makes a real difference to recovery.
- 1
Feeding
Good-quality, easily digested protein in small, frequent portions. If appetite does not return, talk to your veterinarian about an appetite stimulant.
- 2
Hydration
Add more water bowls and set them at a comfortable height. Wet food contributes to hydration too.
- 3
Environment
Somewhere quiet and warm, and as far as possible without moves or visitors during treatment.
- 4
Records
Note weight, appetite, litter tray use and behaviour weekly, under the same conditions each time. That is what makes later decisions possible.
Other cats in the home.FIP does not transmit, but feline coronavirus circulates. Clean litter trays daily and disinfect them periodically with diluted bleach. Separate bowls and keep an eye on the appetite and weight of the others.
The 12-week observation period
Once the 84 days are complete, a 12-week period without medication begins. If no signs of relapse appear, it is considered sustained remission.
- 1
What to watch in that period
That fever does not return, that appetite and weight hold, that energy continues. In cats that had neurological or ocular involvement, that area needs following closely too.
- 2
Relapse Program
We run a support programme for cases that relapse after completing treatment. The conditions are set out on the programme page.
With any change, asking beats waiting.A relapse caught early is far easier to manage. During the observation period you can contact us at any time. View the Relapse Program
About feline infectious peritonitis
How long does treatment last?+
84 days, about 12 weeks, followed by a further 12 weeks of observation without medication. Even if the cat looks perfectly well much earlier, the course is completed: stopping early is the most common cause of relapse.
Injectable or capsules?+
For mild to moderate cases capsules work well. Where there are neurological or ocular signs, digestive problems, or the case is severe, starting with injectables is recommended. Send us the diagnosis and blood work and we will help.
Will it spread to my other cats?+
FIP will not. What transmits is feline coronavirus, through shared litter trays and bowls and through grooming. The mutation that causes FIP happens inside each cat individually.
My cat never goes outside. How did it get ill?+
Because feline coronavirus is everywhere. Most cats are infected as kittens, in catteries, shelters or multi-cat homes. It has nothing to do with the care you give now.
Which cats are most at risk?+
It is seen more in cats under 2 years, males, pedigree cats and cats from multi-cat environments. That said, it can occur at any age in any cat.
Are there side effects?+
In most cases few significant effects are reported. With injectables there can be pain or swelling at the injection site. If anything concerns you, do not stop on your own: speak to your veterinarian first.
How is the dose calculated?+
By weight and by the form of FIP. Neurological and ocular forms need higher doses. Use the dosage calculator as a reference and settle the final dose with your veterinarian. If the cat gains weight during treatment, it needs recalculating.
Can it return after treatment?+
Most cats that complete the 84 days and get through the 12-week observation period go on to live normally. Relapses can happen, which is why we ask for records during observation and contact as soon as you notice anything different.
If your question is not here, see the FAQ.
If the diagnosis has just come through, sooner is better
Feline infectious peritonitis is treatable. More than 100,000 cats have recovered worldwide since 2019. Treatment can start now, delivered to your door across the Gulf.
This page is general information and does not replace veterinary consultation. Diagnosis and the treatment plan are always decided with your veterinarian. Related pages: FCV guide · FHV-1 guide