78.3% Remission in Cats That Had Already Relapsed: Results from a CureFIP Dual Antiviral Study

A field evaluation of 46 cats treated with combined oral GS-441524 and EIDD-1931 shows promising outcomes, even in Feline Infectious Peritonitis (FIP) cases that had previously failed single-drug treatment.

Why This Study Matters

Most published research on Feline Infectious Peritonitis (FIP) treatment evaluates cats receiving antiviral therapy for the first time. But what about the cats that did not respond to their initial treatment? What about the ones that relapsed after completing a full course of GS-441524?

These are the hardest cases. And they are exactly the cats that the BasmiFIP dual antiviral study set out to help.

78.3% Remission in Cats That Had Already Relapsed: Results from a CureFIP Dual Antiviral Study

In a 2024 field evaluation conducted by Li and Cheah under the CureFIP initiative, 46 cats diagnosed with Feline Infectious Peritonitis (FIP) were treated with a co-formulated oral capsule combining GS-441524 and EIDD-1931, two antivirals that attack the virus through completely different mechanisms. The results provide real-world evidence that dual antiviral therapy works, even in the most challenging situations.

The Study: What Was Done

Between June and September 2024, 46 domestic cats diagnosed with Feline Infectious Peritonitis (FIP) were enrolled in the study. The cats represented a broad range of breeds, ages, and Feline Infectious Peritonitis (FIP) types, including wet (effusive), dry (non-effusive), neurological, and ocular presentations. Approximately 90% were indoor-only cats.

Each cat received a standardized oral capsule containing both GS-441524 (at 10-15 mg/kg once daily) and EIDD-1931 (5 mg for cats under 4.5 kg, or 10 mg/kg for cats 4.5 kg and above). Treatment lasted 60 days, with one capsule administered per 2.5 kg of body weight every 24 hours.

Critically, a significant number of the cats in this study had previously relapsed after completing GS-441524 monotherapy. This means the cohort was not made up of easy first-time cases. Many of these cats had already been through treatment, watched it fail, and needed a second chance.

Owners tracked their cat's progress daily, recording weight, appetite, clinical signs, and any side effects. Veterinary validation was obtained where possible. Cats were followed for 180 days after treatment completion to monitor for relapse.

The Results: What Happened

78.3% achieved clinical remission. Of the 46 cats treated, 36 reached full clinical remission following the 60-day dual antiviral protocol. That means no remaining Feline Infectious Peritonitis (FIP) symptoms after treatment.

Only 6.5% relapsed. During the 180-day follow-up period, just 3 of the 46 cats experienced a return of Feline Infectious Peritonitis (FIP) symptoms. This is a notably low relapse rate, especially considering that many of these cats had already relapsed once before on single-drug therapy.

10.9% mortality. Five cats did not survive. The authors noted these deaths were likely due to advanced disease stages or secondary complications at the time treatment began, reinforcing the importance of starting treatment as early as possible.

91% showed weight gain and improved appetite. By mid-treatment, 42 of the 46 cats had documented weight gain and appetite improvement, tracked through individual daily logs. These are strong indicators that the treatment was working and the cats' bodies were recovering.

A:G ratio improved significantly. The albumin-to-globulin ratio, a key blood marker used to track Feline Infectious Peritonitis (FIP) progression, improved from approximately 0.35 at baseline to 0.62 by Day 60. This upward trend indicates that the inflammatory response driven by the Feline Infectious Peritonitis (FIP) virus was progressively resolving during treatment.

Minimal side effects. Only 2 of the 46 cats experienced adverse events, both minor gastrointestinal issues and brief lethargy during early dosing. No severe toxicity was observed, and no cat had to stop treatment due to side effects.

Why These Results Are Significant

The headline remission rate of 78.3% might appear lower than the ~92% typically reported for GS-441524 monotherapy. But context matters enormously here.

Many of the cats in this study were not first-time treatment cases. They were cats that had already relapsed after completing GS-441524 alone, meaning the virus had likely developed some degree of resistance to the drug. Treating resistance cases is inherently harder than treating naive cases, and achieving a 78.3% remission rate in this population is a meaningful result.

The very low relapse rate of 6.5% is particularly encouraging. For comparison, published GS-441524 monotherapy studies report relapse rates of approximately 10-11%. The fact that the dual protocol achieved lower relapse rates in a harder-to-treat population suggests that the combination of GS-441524 and EIDD-1931 provides stronger and more durable viral suppression.

The mechanism behind this makes pharmacological sense. GS-441524 works by stopping the virus from copying itself (chain termination). EIDD-1931 works by introducing fatal errors into whatever copies the virus does manage to produce (lethal mutagenesis). Together, they attack the virus from two completely different angles, making it far more difficult for the virus to develop resistance to both simultaneously.

What This Means for Your Cat

If your cat has been diagnosed with Feline Infectious Peritonitis (FIP), this study adds another layer of evidence supporting dual antiviral therapy. The key takeaways are:

• Dual therapy works in difficult cases. Even cats that had relapsed after GS-441524 monotherapy showed strong recovery rates when treated with the GS-441524 + EIDD-1931 combination.

• The relapse rate is low. At just 6.5% over 180 days of follow-up, the dual protocol showed strong durability against viral recurrence.

• It is well-tolerated. With only 2 minor adverse events across 46 cats and no treatment discontinuations, the safety profile of the combined oral capsule is reassuring.

• Early treatment still matters. The cats that did not survive were generally those with the most advanced disease at the time of enrollment. Starting treatment promptly remains the single most important factor in Feline Infectious Peritonitis (FIP) outcomes.

• The oral format supports compliance. The study used a single daily capsule combining both antivirals, which simplifies the treatment routine and helps cat owners maintain consistency throughout the full course.

Study Limitations

The authors acknowledge that this was an observational field study, not a randomized controlled trial. There was no control group, and outcome data was partly based on owner reports. Pharmacokinetic studies and randomized comparative trials are needed to further validate these preliminary results. However, the consistency of the outcomes across diverse Feline Infectious Peritonitis (FIP) phenotypes and the inclusion of previously relapsed cats make this a valuable contribution to the growing evidence base for combination antiviral therapy.

Conclusion

The CureFIP field evaluation by Li and Cheah (2024) provides real-world evidence that a combined oral regimen of GS-441524 and EIDD-1931 can achieve meaningful remission rates even in the most challenging Feline Infectious Peritonitis (FIP) cases, including those that have already relapsed on single-drug therapy. With minimal side effects, strong weight recovery trends, and a low relapse rate, the dual antiviral approach holds potential as a next-generation standard in Feline Infectious Peritonitis (FIP) treatment.

Feline Infectious Peritonitis (FIP) is no longer the end of the road. For cats that need a second chance, dual antiviral therapy may be the answer.

To learn more about dual antiviral treatment or to consult about your cat's Feline Infectious Peritonitis (FIP) treatment plan, visit curefip.com.

The CureFIP team offers free consultations. Because when every day matters, having the right support makes all the difference.

Read the Full Study

Want to dive deeper into the methodology, data, and clinical analysis? Download or read the complete research paper.

Download Full Study (PDF) | Read Full Study Online

"Enhancing FIP Therapeutic Outcomes: A Field-Based Evaluation of Combined Oral GS-441524 and EIDD-1931 Protocols" by Li, Y. & Cheah, B. (2024). BasmiFIP Initiative.

Reference: Li, Y. & Cheah, B. (2024). Enhancing FIP Therapeutic Outcomes: A Field-Based Evaluation of Combined Oral GS-441524 and EIDD-1931 Protocols. BasmiFIP Initiative.