FIP: Treatment Options for A Once Terminal Diagnosis

Feline infectious peritonitis, or FIP, is every cat guardian’s worst nightmare. Previously untreatable with 100% death rate, it used to be a death sentence, but new treatment options are now available. FIP is particularly devastating because it disproportionately affects young kittens and senior cats.

How do cats get FIP?

FIP is a viral infection that cannot be transmitted directly, but instead is contracted through a feline coronavirus infection. Feline coronavirus (FeCV) is also a viral infection that is transmitted directly between cats and is most commonly asymptomatic –– the infected cat shows no symptoms. Rarely, cats may show mild gastrointestinal disease like diarrhea, or upper respiratory symptoms like sneezing or congestion.

FeCV is self-limiting, meaning a cat’s immune system will take care of the infection and create antibodies against it. Unfortunately, in approximately 10% of cats, feline coronavirus will mutate and cause a system wide infection of the body’s white blood cells — this is FIP.

FIP cats and kittens become very sick, often with multiple organ systems affected including the brain, eyes, and kidneys. Diagnosis of FIP includes blood work which may show an elevation of white blood cells and kidney values, and/or abnormal protein levels which can increase the suspicion of FIP along with the pet’s history and physical exam findings.

How is FIP diagnosed? Does FIP come in different forms?

A definitive diagnosis is made by obtaining a sample of diseased tissue, either fluid or biopsy, and submitting it for specific testing. FIP is often defined in two forms –– the wet form and the dry form.

Wet Form

Cats with the wet form of FIP have fluid in abnormal places including around the lungs in their chest, or around their organs in the abdomen. It’s called wet because it’s defined by fluid or liquid.

When this fluid is sampled, it typically has a ‘straw’ or medium yellow color and is thick like mucus or syrup. As recent as 2015, FIP PCR (polymerase chain reaction) testing of these fluids was introduced to allow for a positive or negative test result. FIP PCR testing can be performed on fluid or tissue samples, and even nasal swabs. It cannot be performed on blood or urine at this time.

This form of FIP is more common.

Dry Form

Cats with the dry form of FIP can be harder to diagnose because there is no fluid to find, collect and test. A biopsy from the affected organ, if possible, can be submitted for testing. A definitive diagnosis may not be possible through testing if an organ like the brain or eye is not safe to sample. Instead, FIP may be suspected when organ systems are suddenly affected or neurologic symptoms including abnormal behavior, dull mentation, or seizures, are observed.

Instead, a positive response to treatment is sometimes the only way to confirm an FIP diagnosis. This means that FIP is suspected and treatment is started without a confirmed test result. A positive response to treatment can include resolution of concerning symptoms, weight gain, and/or improvement in abnormal lab work.

New Treatment and How Effective It Is

Up until 2009, no known treatment was available for FIP. This meant that affected cats were treated symptomatically (i.e. given antinausea for vomiting, anticonvulsants for seizures, etc.). Ultimately, these cats would waste away and eventually die.

Thankfully in 2009, Gilead Sciences, Inc. patented a molecule called GS-441524. Although th molecule was initially for the treatment of hepatitis, it was also eventually targeted for post-infection treatment of COVID-19 as the active ingredient in Remdesivir. The injectable form of this drug is not yet FDA-approved in the United States, but is widely used. It can be obtained in other ways by feline advocates and community members. But as of June 2024, the oral form is readily available and FDA-approved in the United States of America.

GS-441524 is an antiviral compound and it is prescribed for a minimum of 12 weeks in cats with FIP. The dosages can vary depending on the organ affected. Baseline and recheck lab work is recommended, along with a 12 week post-treatment observation period to monitor for signs of relapse. The cure rate of GS-441524 is approximately 80% and a cure is more common in cats younger than 7 years old.

The approximately 20% of cats that do not respond as expected to treatment can be due to a misdiagnosis, inadequate dosing, drug resistance or concurrent diseases.

Not every cat responds to treatment, but now there is hope for cats with FIP — many making a full recovery with no relapse.

What if my one cat gets FIP, can they live with my other cats?

If your cats already lived together prior to diagnosis, it is likely that they both have feline coronavirus (FeCV). This precursor virus mutates into FIP in approximately 10% of cats. It is a good idea to get your other cat tested if their housemate has been diagnosed with FIP. If you are considering bringing a new cat to the home, the risk of them catching it remains low.

Can my veterinarian help with FIP treatment, or do I need a specialist?

FIP can be managed by any veterinarian familiar with an FIP diagnosis, treatment and monitoring. Some veterinarians take a special interest in the disease, and are more comfortable with the care required. A specialist is not necessarily needed for FIP care, but it is important to have a conversation with your vet about what is needed and ensure that they can accommodate the intensive schedule needed for caring for FIP.

How do I know if my cat is cured?

Blood work and examinations are recommended at 4, 8 and 12 weeks during treatment and then 4, 8, and 12 weeks after FIP treatment has been discontinued. The most important parameters are your cat’s wellness: appetite, energy level and return to normal behaviors, along with blood work values returning to a normal (pre-FIP) range.

A relapse during or after treatment is possible, but the risk is low. If relapse occurs during treatment, a higher dose of GS-441524 is recommended. If relapse occurs after treatment, a repeat course of 84 days of treatment, or longer, is recommended.

Can I prevent my cat from getting FIP?

FIP prevention includes prevention of your cat contracting feline coronavirus. This may include quarantining and testing new cats to the household to ensure they are no longer able to spread the disease. Most cats clear feline coronavirus when infected, but some persistently remain infected, and can shed (spread) the virus intermittently.

Keeping your cat healthy with a strong immune system includes a healthy diet, clean environment, and reducing overcrowding and stress. Although an FIP vaccine exists, it is not recommended due to the risk of enhanced disease symptoms if FIP occurs called antibody-dependent enhancement.

My cat was just diagnosed with FIP, what next?

Reach out to your veterinarian as soon as possible to discuss treatment options and supportive care. A well-known and trusted resource is available through FIP Warriors, a group of community members and veterinarians providing support through FIP diagnosis and treatment. Always remember to receive treatment recommendations for your pet directly from your veterinarian.

Having your cat diagnosed with feline infectious peritonitis (FIP) can be shocking. It is important to decide on care for your cat as soon as possible. Do not wait to reach out to your vet to start FIP treatment and care.

If your cat was diagnosed with feline infectious peritonitis (FIP) or you have concerns about their care or comfort, please reach out to us today. We would be honored to help you and your pet through this process.