Feline infectious peritonitis (FIP) is a complex and historically fatal disease, though recent advances in antiviral therapy have uncovered potential treatments. A newer therapeutic option, unlicensed molnupiravir, is being used as a first-line therapy for suspect FIP and as a rescue therapy to treat cats who have persistent or relapsed clinical signs of FIP after GS-441524 and/or GC376 therapy. Using owner-reported data, treatment protocols for 30 cats were documented. The 26 cats treated with unlicensed molnupiravir as a rescue therapy were treated with an average starting dosage of 12.8 mg/kg and an average ending dosage of 14.7 mg/kg twice daily for a median of 12 weeks (IQR = 10–15). In total, 24 of 26 cats were still living disease-free at the time of writing. One cat was euthanized after completing treatment due to a prolonged seizure, and the other cat underwent retreatment for relapsed clinical signs. Few adverse effects were reported, with the most notable—folded ears (1), broken whiskers (1), and severe leukopenia (1)—seen at dosages above 23 mg/kg twice daily. This study provides a proof of principle for the use of molnupiravir in cats and supports the need for future studies to further evaluate molnupiravir as a potentially safe and effective therapy for FIP.

Introduction: Feline Infectious Peritonitis (FIP) has historically been a fatal coronavirus disease in cats. In recent years, the therapeutic agent GS-441524, developed by Gilead Sciences, was found to be a successful treatment for FIP in most patients in clinical trials. However, this particular drug has remained stalled in the therapeutic pipeline, leaving patients and cat owners without a licensed medication. In the meantime, online social media platforms began to emerge, connecting cat owners with a community of citizen non-veterinary professionals sourcing unlicensed GS-441524.Methods: This study prospectively followed participants (N = 141) that successfully completed 12 weeks of treatment, capturing their treatment experiences with self-administered GS-441524-like medication. A one-time survey was administered to enrolled participants with mixed format of questions (open-ended and multiple-choice) asking about treatment administration techniques, observed side effects of GS-441524, accrued cost, veterinarian involvement, impact on the cat-human bond, and social media usage.Results: Our results show cat owners experienced a shift in treatment modality from injectable GS-441524 to pill formulation across the treatment period. The average total cost of medication has decreased since 2021 to approximately USD 3100, and participants reported the human–animal bond being affected negatively. Additionally, there was an increased trend in veterinarian awareness of GS-441524-like therapeutics and monitoring of clients undergoing treatment. Social media usage was reported as being important at the beginning of treatment to establish treatment administration but lessened by the end of treatment.Discussion: This study is the first detailed, prospective account of owner experiences with unlicensed GS-441524, raising an important discussion surrounding citizen veterinary medicine.

Feline Infectious Peritonitis (FIP) is caused by a systemic feline coronavirus (FCoV). Prior to June 2024, compounded FIP treatment was unavailable for prescription by veterinarians in the United States, leading to many cat owners obtaining treatment through unlicensed “black market” sources. We hypothesized that clinicopathologic data could provide insight on prognostic indicators for the treatment of FIP with GS-441524. This study used data gathered via surveys from 126 cat owners who used “black market” GS-441524 for their cats. We compared bloodwork parameters over twelve weeks of treatment. None of the clinicopathologic correlates, when analyzed via two-sample t-tests, produced statistically significant results between cured, deceased, and relapsed groups. Within cats considered cured, it was observed that hematocrit (HCT) and white blood cell (WBC) values were within normal limits by the 2–6-week period. Cats who died during the study had lower HCT and higher WBC values within the 2–6-week period. Trends were also seen in A/G and total bilirubin (T-BIL), with deceased patients showing a higher A/G ratio and lower value than those in the cured group. Overall, these data demonstrate a lack of traditional clinicopathologic parameters which are consistently predictive of FIP therapy success. Other predictors of outcome with antiviral therapy should be pursued.

Background: There is limited information about treatment success and outcomes in retrovirus-positive cats diagnosed with feline infectious peritonitis (FIP). Methods: A survey was distributed to caretakers of cats with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV) that were treated with GS-441524 for presumptive effusive FIP based on survey responses. Results: Cats with FIV developed FIP at an older age and longer after retrovirus infection than cats with FeLV. The average starting dosage (7 mg/kg/d) was increased in 65% of cats, and treatment was extended in 35%. Three cats relapsed (18%). There was a 94% (16/17) twelve-week survival rate and 82% (14/17) one-year survival rate. Seven cats were alive at follow-up, a median of 1306 days (range 983–2069) after FIP diagnosis, but many cats succumbed to neoplasia. Conclusions: Treatment success for retrovirus-positive cats with presumptive FIP was similar to previously reported outcomes for FIP alone. This could support current evidence of successful antiviral therapy for similar populations, if noncurrent, unstandardized protocols and unlicensed product use are considered. Additional studies are needed to determine ideal protocols for rapid resolution of FIP, good long-term survival, and limited relapse in retrovirus-positive cats, and the impact of the FeLV proviral load.