Understanding FIP Relapse: Why It Happens and What to Do

Key Takeaways

• FIP is treatable: GS-441524 has turned FIP from fatal to manageable, with very high recovery rates when used properly.

• Relapse is rare: Only about 3% of cats experience a relapse after completing treatment.

• Relapse vs. reinfection: Relapse is the return of the same infection, while reinfection means exposure to a new strain.

• Early detection matters: Loss of appetite, fever, weight loss, or abdominal swelling after treatment may signal relapse.

• GS-441524 is the best option: Relapse cases require restarting GS-441524 injections, often at higher doses.

• Veterinary supervision is essential: Only licensed veterinarians can confirm relapse and adjust treatment safely.

Not too long ago, hearing the words “your cat has FIP” felt like the end of the road. Feline Infectious Peritonitis (FIP) used to be considered a death sentence for cats, leaving devastated families with no real options.

But everything changed thanks to groundbreaking research—especially the work of Dr. Niels Pedersen at UC Davis in 2018. GS-441524 injections completely rewrote the story. Recovery rates now exceed 92% when treatment is given for the full 84 days. Cats that once had no chance are now living full, happy, and playful lives.

And yet, even with these amazing advances, relapse does sometimes happen. About 3% of cats may show symptoms again after treatment ends. But if you’re a cat parent reading this, don’t panic: relapse doesn’t mean the battle is lost—it just means your cat might need a little extra help.

What Is FIP Relapse?

So, what exactly is relapse?

Relapse means that after finishing treatment—even when your cat seems perfectly healthy—tiny traces of the virus may remain hidden and can flare up again later. Think of it like weeds in your yard—most are pulled out, but a stubborn root can sprout again if it wasn’t completely removed.

This is different from reinfection, which happens if your cat is exposed to a completely new strain of feline coronavirus. According to veterinary studies, including UC Davis and other peer-reviewed research, relapse usually shows up within the first three months after stopping treatment.

The difference in simple terms:

• Relapse: The same FIP infection wasn’t fully cleared and sneaks back.

• Reinfection: Your cat encounters a new strain of the virus from the outside world.

Why does this matter? Because relapse means restarting therapy, while reinfection often calls for prevention strategies in multi-cat households.

Why Does Relapse Happen?

Now comes the big question: why would relapse happen if the treatment worked so well?

Incomplete Viral Suppression

Sometimes, if treatment ends too early, a small amount of the virus can linger in the body. Even tiny traces can regroup and cause symptoms to return. Studies show that completing the full 84 days of therapy (and sometimes longer) gives the virus less chance to bounce back.

Drug Resistance

Viruses are clever survivors. Under the pressure of medication, feline coronavirus can mutate, making it harder for the same treatment to wipe it out completely. When this happens, higher doses of GS-441524 are usually needed to outsmart the virus.

Dosing Mistakes and Compliance Issues

FIP treatment can feel overwhelming. Missed doses, under-dosing, late or inconsistent timing, or splitting capsules incorrectly can all give the virus room to rebound. Research shows precise, consistent dosing is absolutely critical. Veterinary-prepared GS-441524 formulations make this easier and reduce mistakes.

So while relapse can be frightening, it isn’t purely random. Beyond treatment issues and viral resistance, outside triggers like stress or another illness during the observation period can also play a role.

Early Signs of FIP Relapse

Relapse often whispers before it shouts. Keep an eye out for these signs after treatment ends:

• Loss of appetite or refusing food

• Weight loss, even if your cat seems to be eating

• Recurrent fevers above 103.1 °F (39.5 °C)

• Swollen belly or fluid buildup

• Neurological signs: wobbling, seizures, or unsteady walking

• Eye changes: cloudiness, inflammation, lethargy, or a strange glow

⚠️ If you see any of these signs, don’t wait. Cats are masters at hiding illness, so by the time symptoms are visible, urgent veterinary care is needed. Getting your cat to the vet right away gives them the best chance at a quick recovery.

Treatment Strategies for Relapse

Here’s the good news: relapse is not the end of the road. When relapse happens, the standard approach is to restart GS-441524 injections—this time at a higher dose.

The goal is to fully suppress the virus, even in harder-to-reach tissues like the nervous system and eyes. Treatment length may vary, lasting from 2 weeks for mild relapses up to 12 weeks for more severe cases.

We know relapse can leave cat parents feeling scared, worried, and exhausted after already going through treatment once. That’s why we created the CureFIP™ Relapse Program—to stand with you and your cat every step of the way.

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Summary

• FIP is no longer a death sentence—thanks to GS-441524, most cats recover.

• Relapse is rare (around 3% of cases) but possible.

• Relapse usually happens because of incomplete viral suppression, drug resistance, dosing mistakes, or external triggers like stress or other illnesses.

• Watch for warning signs such as loss of appetite, weight loss, fever, swollen belly, neurological issues, or eye changes.

• The best treatment for relapse is GS-441524 injections at a higher dose, under close veterinary supervision.