GS-441524 is a nucleoside analogue antiviral compound that works by blocking the replication of the feline infectious peritonitis virus (FIPV). When the virus attempts to copy its RNA inside your cat's cells, GS-441524 interferes with that process — stopping the disease at its source rather than just managing symptoms.

It is the most extensively studied treatment for FIP, with clinical recovery rates consistently above 80% across multiple independent studies. Until recently, FIP was considered almost universally fatal. GS-441524 has changed that.

Across multiple independent clinical studies covering over 650 cats, the combined treatment success rate for GS-441524 is approximately 85%. Most cats that complete the full 84-day protocol reach sustained remission and return to a normal quality of life.

Cats that begin treatment earlier in the disease course tend to have the best outcomes. Complicated forms — including neurological and ocular FIP — have a lower but still meaningful recovery rate when treated at higher doses with injections. The key variables are: starting treatment promptly, dosing correctly by weight, and completing the full protocol without interruption.

The earliest signs of FIP are often non-specific and easy to overlook. Persistent fever that does not respond to antibiotics is typically the first indicator. This is usually accompanied by loss of appetite, unexplained weight loss, lethargy, and a dull or unkempt coat. Some cats also develop mild digestive upset in the early stages.

As the disease progresses, more specific signs emerge depending on the form. In wet FIP, a visibly swollen or distended abdomen develops as fluid accumulates. In dry FIP, signs vary more widely and may include neurological changes such as loss of coordination, tremors, or seizures, as well as eye abnormalities like cloudiness or uneven pupil size.

Wet (effusive) FIP is characterised by fluid accumulation in the abdomen or chest cavity, and tends to progress rapidly. Dry (non-effusive) FIP involves inflammatory lesions in organs without significant fluid build-up, and typically progresses more slowly.

Both forms are treated with GS-441524 using the same core protocol. What changes is the starting dose and urgency of treatment. Neurological and ocular FIP — which can occur in either form — require higher doses and must be treated with injections only.

FIP develops when the feline enteric coronavirus (FCoV) — a common intestinal virus that most cats carry without ever falling ill — undergoes a mutation inside the cat's body. This mutation transforms it into the feline infectious peritonitis virus (FIPV), which triggers a severe immune response and attacks the cat's own tissues.

FCoV itself is contagious and spreads between cats through shared litter boxes, food and water bowls, and close contact — particularly in multi-cat households, shelters, and catteries. However, FIP itself does not spread directly from cat to cat. The mutation that causes FIP occurs randomly and cannot be predicted.

FIP itself is not directly contagious between cats. The disease cannot be passed from one cat to another. What is contagious is the underlying feline coronavirus (FCoV) — the common, usually harmless intestinal virus that, in rare cases, mutates inside an individual cat's body to cause FIP. FCoV spreads through shared litter boxes, food and water bowls, grooming, and close contact.

During your cat's FIP treatment, standard hygiene precautions are sufficient: keep litter boxes clean and disinfect them regularly, wash food and water bowls separately, and monitor other cats in the household for changes in behaviour, appetite, or weight.

Yes — with treatment. FIP was once considered almost universally fatal, and without antiviral intervention it still carries an extremely poor prognosis. The median survival time without treatment is approximately 9 days from the point of diagnosis.

With GS-441524 antiviral treatment, the outcome has changed fundamentally. Across multiple independent clinical studies covering over 650 cats, the combined treatment success rate is approximately 85%. The majority of cats that complete the full 84-day protocol reach sustained remission and go on to live normal, healthy lives.

Yes. The majority of cats that complete a full course of GS-441524 treatment go on to live normal, healthy lives. In clinical studies, most cats in sustained remission after the 84-day protocol show no long-term health consequences from the infection itself.

Some cats experience residual effects from organ involvement during the active disease phase — particularly in cases with neurological or ocular complications — but these typically resolve or stabilise after treatment ends.