How long does treatment last?

For years the standard course was 84 days (12 weeks). That length came from early studies rather than proof that 84 days is needed.

The 42-day study

In 2024 a randomised controlled trial treated 40 cats with wet FIP with oral GS-441524 for either 42 or 84 days. Cats that completed the shorter course stayed in remission at the end of follow-up (day 168), and the authors concluded that 42 days was as effective as 84 for those cats. The updated ABCD guidelines now reflect that a shorter course can work for many cats.

Why your cat's plan may differ

• The trial studied cats with wet FIP. Cats with eye or nerve involvement may need longer treatment.
• A follow-up analysis of the same cats noted some differences after the short course, such as lower lymphocyte counts and a few cats shedding virus again, so monitoring still matters.
• Vets usually stop treatment when the cat is well, blood results have normalised, and the inflammation marker AGP is normal, rather than only because a date has arrived.
• Some cats recover more slowly and need longer.

This is why FIP Together lets you enter any duration your vet prescribes, and never marks treatment as finished by itself: only your vet decides when to stop.