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Unlicensed antiviral products used for the at-home treatment of feline infectious peritonitis contain GS-441524 at significantly different amounts than advertised.

Kent AM, Guan S, Jacque N, Novicoff W, Evans SJM. Unlicensed antiviral products used for the at-home treatment of feline infectious peritonitis contain GS-441524 at significantly different amounts than advertised. J Am Vet Med Assoc. 2024 Feb 7;262(4):489-497. doi: 10.2460/javma.23.08.0466. PMID: 38324994.

At one time, Feline Infectious Peritonitis (FIP) was thought of as an incurable and fatal disease. There is now strong evidence that certain therapies are leading to promising outcomes for cats afflicted with this viral disease, bringing hope to many cat owners, shelter personnel, and veterinarians. Unfortunately, in the United States and many other parts of the world, it has been challenging for veterinarians to prescribe these medications, including GS-441524 which is the active metabolite of the COVID-19 treatment remdesivir.

With the help of online and social media support groups, cat owners have been able to access ‘unlicensed’ lifesaving FIP treatment for their beloved pets. Though there is published literature that has demonstrated that these unlicensed therapies are effective, the true contents and pH of these formulations has never been studied. This research article from the Journal of American Veterinary Medical Association (JAVMA) offers new insights for cat owners to hopefully allow them to make better informed decisions about treatment as well as bring to light this unique public health phenomenon.

Note: This report provides a disclaimer that the products evaluated are not legally available in the US and are only available on the black market.

The Numbers:
– 87 injectable and 40 tablet/capsule samples from 30 different brands were procured through donations by cat owners to The Ohio State University College of Veterinary Medicine
– All 127 products contained GS-441524
– The number of samples for each product varied and ranged from 2-9
– 69% percent of the samples were manufactured in China, 14% in the US, 10% in Canada, 4% in Malaysia, 1% in Poland, and 2% from unknown location
– The samples were submitted to the University of California-Davis School of Medicine Molecular Pharmacology Shared Resource for analysis of GS-441524 & Remdesivir concentration as well as the pH of injectable formulations
– 83 of the 87 injectable samples (95%) contained more GS-441524 than the reported concentration on average 39 +/- 17% higher
– 4 of the 87 injectables were on average 18 +/- 8.4% lower; all were made by different manufacturers
– 17 of the 40 oral samples (17%) contained more GS-441524 than reported on average 75 +/- 91.3% higher
– 23 of the 40 oral samples (58%) contained less than reported on average 39 +/- 20% lower
– For those products where multiple samples were available, 6 out of the 8 injectable products had an acceptable variability of under 10%
– 3 products contained remdesivir, with only 1 product advertising this fact
– The pH of the injectable GS-441524 samples was on average 1.30 +/- 0.15

Inside the Numbers
– Based on FDA Good Manufacturing Process regulations, products must contain 95-105% of active pharmaceutical at time of manufacturing; only 2 of the 87 tested injectable samples were within this range
– The authors speculated that producers often include excess drug in their injectable products to intentionally gain a competitive advantage (their product appears more effective) and/or to compensate for poor purification, stability, or lot-to-lot variability
– There was some difficulty in evaluating the oral formulation GS-441524 contents as manufacturers likely report the amount that is bioavailable to the cat instead of the amount that is actually in the pill; This would allow owners to more easily make the transition from injectable to oral treatments
– As oral formulations are becoming more common due to ease of administration, no possibility for injection site reactions, and less expensive over time, there is a risk of insufficient GS-441524 content and the possibility of treatment resistance in some animals may be present
– The finding of remidisivir in some products, whether intentional or not, does highlight the risk of the uncertain quality and purity of unlicensed products
– The average pH of the injectable samples was more acidic than claimed by the producers; A low pH of the product likely causes tissue pathology such as pain and reaction in cats

What does This Research Tell Us?
As unlicensed FIP therapies will continued to be used until legal products are developed and become available, this original research should educate pet parents, shelter personnel, and veterinarians on the variability of black market injectable and oral treatments. Labeling of the oral tablets/capsules is also confusing as the contents are listed unconventionally. In the future, reliably manufactured approved products will benefit the feline patients that desperately need the proper treatment to survive this fatal condition.

See Also:
Jones S, Novicoff W, Nadeau J, Evans S. Unlicensed GS-441524-Like Antiviral Therapy Can Be Effective for at-Home Treatment of Feline Infectious Peritonitis. Animals (Basel). 2021 Jul 30;11(8):2257. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8388366/

Pedersen NC, Jacque N. FIP treatment with oral formula¬tions of GS-441524. University of California-Davis. Updated October 3, 2021. Accessed April 21, 2024. https://ccah.vetmed.ucdavis.edu/sites/g/files/dgvnsk4586/files/inline-files/Use-of-oral-GS-441524-for-FIP-treatment-v10.pdf

Thayer V, Gogolski S, Felten S, Hartmann K, Kennedy M, Olah GA. 2022 AAFP/EveryCat Feline Infectious Peritonitis Diagnosis Guidelines. J Feline Med Surg. 2022 Sep;24(9):905-933. doi: 10.1177/1098612X221118761. Erratum in: J Feline Med Surg. 2022 Sep 6; https://journals.sagepub.com/doi/10.1177/1098612X221118761