FIP treatment: what the current evidence actually shows (cure rates, dose, and relapse)

Short answer: across the published studies, antiviral treatment built on GS-441524 puts roughly 80–95% of treated cats into lasting remission over a standard 84-day (12-week) course, with relapse now reported in only a small minority. Oral molnupiravir performs comparably to injectable GS-441524 in head-to-head data. The main threats to a good outcome are late diagnosis, under-dosing (often from unregulated product), and the harder-to-reach neurological and ocular forms.

This is one of the most dramatic reversals in veterinary medicine. A decade ago, an FIP diagnosis was effectively a death notice. Today the honest headline is the opposite — and it is backed by a growing body of published outcomes, not just anecdote.

The cure rates, with sources

• A systematic review of GS-441524 (2018–2024) put overall treatment success at about 84.6% across the accumulated literature. Read on PMC
• A 2020–2024 outcomes analysis reported a survival rate of 94.12% with a relapse rate of just 0.63% in its cohort. Read on PMC
• A head-to-head study found GS-441524 and molnupiravir similarly effective: 48 of 48 cats on GS-441524 and 51 of 52 on molnupiravir reached remission, with comparable safety. Read on Frontiers
• A 2025 case series of 54 cats treated with oral molnupiravir reported strong outcomes over a median 84-day course. Find on PubMed

Put together: the large majority of cats that are diagnosed and treated properly survive and stay well. That is the number to hold onto.

What "treatment" actually involves

• A defined course, usually 84 days (12 weeks). Daily dosing, every day, without gaps — consistency is one of the strongest predictors of success.
• A dose set by weight, form, and severity. GS-441524 is dosed higher for wet FIP than mild dry FIP, and higher still for ocular and neurological FIP, because the drug must reach the eye and the brain. This is exactly why a single "mg/kg" number off a website is dangerous — see our note on why we won't hand you one.
• A watch period after. Once the course ends, an observation period (commonly around 12 weeks) checks for relapse before a cat is called cured.
• Monitoring throughout. Recovery is tracked on clinical signs and bloodwork — weight, the globulin level and A:G ratio, red-cell count, and bilirubin all trend back toward normal as the cat responds.

Use the treatment calculator to see how weight and form change a dose — as an educational estimate, never a prescription.

Oral vs injectable — the short version

Both routes work. Injectable GS-441524 was the original backbone and gives reliable blood levels, but the injections can sting and, with some unregulated products, cause sores. Oral options — oral GS-441524 and molnupiravir — have made treatment far kinder, and the comparative data show similar efficacy. Many modern protocols start injectable and transition to oral, or run oral throughout. We go deeper in oral vs injectable evidence.

Where outcomes get harder

The averages hide real variation. Outcomes are worse when:

• Diagnosis comes late, after the cat is already very sick.
• The neurological form is involved — the blood–brain barrier makes adequate dosing harder, and these cats need higher doses and careful monitoring.
• The dose is wrong — which, given the unregulated market, is a genuine and underappreciated risk. Independent testing of unlicensed products found some containing far less GS-441524 than labelled, and others far more. We cover that study and its implications here.

Relapse and re-treatment

Relapse — technically recrudescence — happens in a minority, often within the watch period, and frequently responds to restarting treatment, usually at a higher dose or for longer. A relapse is not the end of hope; it is a known, manageable part of the picture for some cats.

The bottom line

If your cat has FIP and can be treated, the odds are genuinely in your favour — more so than almost anything else this word used to mean. The work now is getting a correct diagnosis, a correct dose from a trustworthy source, and the full course completed under veterinary supervision.

Next, understand the drug at the centre of all of it: GS-441524.

Not veterinary advice. Cure rates are population figures; your cat's treatment is a decision for a veterinarian who has examined them.

References

1. Efficacy of GS-441524 for feline infectious peritonitis: a systematic review (2018–2024). Read on PMC
2. Analysis of risk factors, clinical data, and treatment outcomes for cats with FIP using GS-441524 (2020–2024). Read on PMC
3. GS-441524 and molnupiravir are similarly effective for the treatment of cats with FIP. Frontiers in Veterinary Science, 2024. Read on Frontiers
4. Clark et al. Treatment of feline infectious peritonitis in cats with molnupiravir: clinical observations and outcomes for 54 cases. Australian Veterinary Journal, 2025. Find on PubMed