Oral Presentation 24th International Conference of Racing Analysts and Veterinarians 2026

Pharmacokinetics of metformin in horses and potential exposure through environmental contamination (130311)

Megan E Jacobs 1 , Jeff Blea 2 , Michael Hardy 3 , Megan Traynham 1 , Daniel S McKemie 1 , Heather K Knych 1
  1. KL Maddy Equine Analytical Chemistry Lab -Pharmacology Section, Davis, CALIFORNIA, United States
  2. School of Veterinary Medicine, University of California, Davis, Davis, California, United States
  3. Racing Medication and Testing Consortium, Lexington, Kentucky, United States

Although not commonly used in horses, metformin, a prohibited substance, is one of the most widely prescribed medications in human medicine raising concerns over the potential for exposure from environmental contamination. Recent reports of metformin in post-race blood and urine samples collected from horses at racetracks in the United States necessitates further investigation of this compound. Twelve exercised Thoroughbred horses were administered metformin orally and intravenously in a randomized, balanced, two-way crossover design. Serum and urine samples were collected post administration and drug concentrations determined via liquid chromatography-tandem mass spectrometry. Data was analyzed using both non-compartmental and population PK analysis. In a separate study, 6 horse stalls were contaminated with urine containing metformin at known concentrations. Blood and urine samples were collected over 72 hours and metformin concentrations determined.  In the administration study, metformin concentrations were below the LOQ (0.25 ng/mL) in 6 of 12 horses at 264 hours (day 11) post administration, and below the LOQ for all 12 horses at 600 hours (day 25). The mean (± SD) maximum serum concentration of metformin was 941.0 ± 467.8 ng/mL, and the mean (± SD) terminal t1/2 was 85.5 ± 11.6. Based on Monte Carlo simulations the time that serum metformin concentrations fell below the proposed HISA Anti-Doping and Medication Control minimum reporting level (0.5 ng/mL)in a simulated population of 1000 Thoroughbred horses, was 13 days. Metformin concentrations in urine fluctuated significantly between individual horses. Albeit at low concentrations, metformin was detected in blood and urine samples collected from horses housed in metformin contaminated stalls. The results of the present study suggest that a prolonged detection time and subsequently withdrawal time is needed for blood to prevent an adverse analytical finding following administration and that detection of low levels of metformin are possible as a result of environmental exposure.