What Is the Best Treatment for FIP in Cats?

The best treatment for Feline Infectious Peritonitis (FIP) in cats is antiviral therapy built around GS-441524, given daily under your veterinarian's care for a full 84-day (12-week) protocol. In a UC Davis clinical trial, GS-441524 reached a 92% success rate, and since 2019 more than 100,000 cats have been treated. FIP, once considered hopeless, now has a clear and trusted path to remission.

What Is the Best Treatment for FIP in Cats?

If you are reading this after a frightening diagnosis, take a breath. You are not the first Pawrent to face FIP, and your cat's odds are better than they have ever been. Below, we walk you through what FIP is, which treatment fits each form of the disease, and how to start your cat's recovery journey alongside your veterinarian.

What is the best treatment for FIP in cats?

The best treatment for FIP is GS-441524 antiviral therapy, the hero ingredient in the BasmiFIP line, given daily for an 84-day (12-week) course under veterinary supervision. GS-441524 reached a 92% success rate in a UC Davis clinical trial, and it remains the foundation of FIP recovery worldwide. For some forms of FIP, your veterinarian may combine or sequence GS-441524 with EIDD-1931, a second antiviral that is roughly 7.3 times more potent than GS-441524.

There is no single pill that works for every cat. The right plan depends on which form of FIP your cat has, your cat's weight, and how your cat is responding. That is why diagnosis and veterinary guidance come first. The good news is that the core medicine, GS-441524, is the same proven antiviral that tens of thousands of families have already trusted.

What are the four forms of FIP, and why does it matter?

FIP has four forms: wet (effusive), dry (non-effusive), neurological, and ocular. Each form behaves differently, and the form decides which medicine and which dose your cat needs. Neurological FIP and ocular FIP are two separate forms, not one combined category.

• Wet (effusive) FIP: Fluid builds up in the belly or chest. This is often the fastest-moving form.

• Dry (non-effusive) FIP: No major fluid buildup, but inflammation forms in organs. It can be slower and harder to spot.

• Neurological FIP: The virus affects the brain and spinal cord, causing wobbliness, seizures, or behavior changes.

• Ocular FIP: The virus affects the eyes, causing color changes, cloudiness, or vision problems.

Why does this matter? Because the dose of GS-441524 rises with the severity and location of the disease. Neurological and ocular FIP need higher doses to reach the brain and eyes, where the virus is harder to treat.

How does GS-441524 treatment work for FIP?

GS-441524 is a daily antiviral that stops the FIP virus from copying itself, given as an injection every day for the full 84-day (12-week) protocol with no skipped days. The BasmiFIP GS-441524 injectable is 40 mg/ml at 99.4% purity in an 8 ml vial, and your veterinarian calculates the exact daily dose from your cat's current weight.

The dose depends on the form of FIP:

FIP form

GS-441524 daily dose

Route

Wet (effusive)

6 mg/kg

Daily injection

Dry (non-effusive)

8 mg/kg

Daily injection

Ocular

10 mg/kg

Daily injection

Neurological

10 mg/kg

Daily injection

Because cats often gain weight as they recover, your veterinarian should reweigh your cat regularly and adjust the dose upward. Under-dosing is one of the most common reasons treatment stalls, so steady weekly check-ins matter.

Are there oral options instead of daily injections?

Yes, BasmiFIP offers oral antiviral options, but they are used for specific situations and not as a replacement in every case. Daily GS-441524 injections remain the foundation, especially at the start and for ocular or neurological FIP.

The oral choices are:

• EIDD-1931 oral capsules: 15 mg per capsule, 60 capsules per box. These are indicated for wet (effusive) and dry (non-effusive) FIP only. They are not for ocular or neurological FIP, and not for cats that are not eating or defecating normally.

• Dual Antiviral oral capsules (GS-441524 + EIDD-1931): One capsule per day. These are used after about 30 days of injections or once your cat is stable. They are not used during ocular or neurological symptoms, not during vomiting or diarrhea, and not for cats under 1 year with wet FIP.

EIDD-1931 dosing by weight is one capsule every 12 hours per 2.5 kg of body weight:

Cat weight

EIDD-1931 capsules

Under 2.5 kg

1 capsule every 12 hours

2.5 to 5 kg

2 capsules every 12 hours

Over 5 kg

3 capsules every 12 hours

The Dual Antiviral capsule strength also follows weight bands: under 2.5 kg is GS 25 mg + EIDD 5 mg; 2.5 to 5 kg is GS 35 mg + EIDD 8 mg; over 5 kg is GS 50 mg + EIDD 10 mg, all once per day.

Important safety note: EIDD-1931 is potentially teratogenic. It must never be given to pregnant, nursing, or breeding cats. Always confirm your cat's status with your veterinarian before starting any EIDD-1931 product.

Which treatment path fits my cat's form of FIP?

The treatment path depends on whether your cat has ocular or neurological signs, and on how your cat is eating and pooping. Here is the general logic your veterinarian will follow.

1. Wet or dry FIP, no ocular or neurological signs: Your veterinarian may start EIDD-1931 for 30 days. If symptoms persist, the course can be extended. If symptoms continue past 60 days, the plan switches to GS-441524 at 10 mg/kg.

2. Ocular or neurological FIP, or a cat not eating and pooping normally: Start with GS-441524 injections for 30 days. Once your cat is stable, your veterinarian may switch to the GS-441524 Dual Antiviral capsule.

Here is a simple summary:

Situation

Suggested start

Notes

Wet or dry FIP, no eye or brain signs

EIDD-1931 for 30 days

Extend if needed; switch to GS-441524 at 10 mg/kg if symptoms pass 60 days

Ocular or neurological FIP

GS-441524 injections, 10 mg/kg

May move to Dual Antiviral capsule once stable

Cat not eating or pooping normally

GS-441524 injections

Avoid EIDD-1931 capsules until eating and defecating normally

This is a guide, not a prescription. Your veterinarian tailors the exact plan to your individual cat.

What success rate can I expect from FIP treatment?

GS-441524 reached a 92% success rate in a UC Davis clinical trial, and that figure is the most widely cited measure of how far FIP treatment has come. For combined therapy, a dual-antiviral field study (Li and Cheah 2025) reported a 78.3% remission rate using GS-441524 together with EIDD-1931.

These two numbers come from different studies and different protocols, so we keep them separate. What both show is the same encouraging truth: FIP is now a treatable disease for most cats, and the track record of more than 100,000 cats treated since 2019 backs that up. We never call this a cure, and no honest source can promise a guaranteed outcome, but the path to remission is real and well-traveled.

How long does FIP treatment take?

The standard FIP protocol lasts 84 days, which is 12 weeks of daily antiviral treatment with no skipped days. After the 84 days, your veterinarian usually monitors your cat through an observation period to confirm the disease stays in remission.

Consistency is everything. Missing doses or stopping early gives the virus a chance to return, so plan your supplies and your schedule for the full 12 weeks before you begin. Many families find it helpful to keep a simple daily log of weight, dose, appetite, and energy.

What should I avoid during FIP treatment?

During FIP treatment, avoid certain medicines and supplements that can interfere with the antiviral or stress your cat's system. Always clear every product with your veterinarian first.

Avoid the following during treatment:

• Fluoroquinolone antibiotics

• Spot-on (topical) flea medications

• Lysine supplements

• Immune boosters

These can complicate recovery or work against the treatment. If your cat needs antibiotics or parasite control during the protocol, your veterinarian can choose safer alternatives.

Can supportive supplements help during FIP treatment?

Supportive nutraceuticals like LiverRx and KidneyRx can help support organ health during treatment, but they are adjunct support only and do not treat the FIP virus. They are never a substitute for GS-441524 antiviral therapy.

• LiverRx (cats and small dogs): Contains SAMe 90 mg, Silybin A+B (milk thistle) 9 mg, Vitamin E 13 mg, and Vitamin C 10 mg, with 30 tablets per box. It is intended to support liver health.

• KidneyRx (cats and dogs): Contains Magnesium carbonate 10 mg, Vitamin D 50 IU, Calcium carbonate 15 mg, L-Carnitine 25 mg, Chitosan 25 mg, Omega-3 50 mg, and Cranberry extract 25 mg, with 60 tablets per box. It is intended to support kidney health.

Think of these as helpers for the organs that work hard during recovery, used alongside the antiviral plan your veterinarian sets, not in place of it.

How do I start my cat's FIP recovery journey?

Start by confirming the diagnosis with your veterinarian, then begin the right antiviral protocol as soon as possible. FIP moves quickly, so early action gives your cat the best chance.

1. Get a clear diagnosis. Ask your veterinarian to confirm FIP and identify the form (wet, dry, neurological, or ocular).

2. Weigh your cat accurately. The dose depends on current weight, so a precise number matters from day one.

3. Choose the protocol with your veterinarian. Match the medicine and dose to your cat's form of FIP.

4. Commit to the full 84 days. Plan supplies and a daily schedule before you begin.

5. Track and recheck. Log weight and symptoms, and reweigh regularly to keep the dose correct as your cat grows stronger.

There is a clear path forward, and it starts with the right diagnosis. You do not have to walk it alone, and we will help you understand each stage alongside your veterinarian.

FAQ

What is the best treatment for FIP in cats?

The best treatment is GS-441524 antiviral therapy given daily for the full 84-day (12-week) protocol under your veterinarian's care. GS-441524 reached a 92% success rate in a UC Davis clinical trial, and for some cats your veterinarian may combine it with EIDD-1931.

Can FIP be treated without injections?

For wet or dry FIP without ocular or neurological signs, your veterinarian may use EIDD-1931 oral capsules or the GS-441524 Dual Antiviral capsule once the cat is stable. However, ocular and neurological FIP, and cats not eating or pooping normally, should start with daily GS-441524 injections.

How long does FIP treatment last?

The standard FIP protocol lasts 84 days, which is 12 weeks of daily antiviral treatment with no skipped days. Your veterinarian usually adds an observation period afterward to confirm the disease stays in remission.

Is FIP treatment safe for a pregnant cat?

EIDD-1931 is potentially teratogenic and must never be given to pregnant, nursing, or breeding cats. Tell your veterinarian if your cat is or could be pregnant so the plan can be adjusted safely.

What should I avoid giving my cat during FIP treatment?

Avoid fluoroquinolone antibiotics, spot-on flea medications, lysine supplements, and immune boosters during treatment. Always check every medicine and supplement with your veterinarian first, since safer alternatives are usually available.