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Investigation of Metformin Contamination in Horses: Implications for Environmental Exposure and Doping Control
Megan E Jacobs1, Jeff Blea2, Michael Hardy3
1K.L. Maddy Equine Analytical Chemistry Laboratory (Pharmacology Section), School of Veterinary Medicine, University of California, Davis, California, USA.
Abstract:
Metformin is a diabetes medication with minimal therapeutic efficacy in veterinary medicine. However, recently there have been several adverse analytical findings in regulatory samples collected from racehorses. Metformin is commonly prescribed to humans, is excreted unchanged in urine, and is resistant to environmental degradation, raising concerns with respect to environmental contamination. In this study, six horses were exposed to shavings contaminated with metformin-positive urine at concentrations of 10, 135, and 270 μg/mL. Blood (plasma, serum, whole blood, and red blood cells) and urine samples were collected for 168 h post-exposure for determination of metformin concentrations. All horses had detectable metformin concentrations in blood samples at least once during the sample collection period. Metformin concentrations in urine samples greatly exceeded those in blood and were detectable as early as 4 h post-contamination. The presence of metformin in these samples raises the possibility of metformin exposure through contamination, especially given the housing conditions at racetracks. The potential for exposure through contamination, resulting in adverse analytical findings, should be considered in the regulation of metformin in racehorses.
Insights
Metformin, a human diabetes drug, was detected in racehorses through environmental contamination. This study shows horses can absorb metformin from contaminated bedding, leading to adverse analytical findings in regulatory samples.
Area of Science:
- Veterinary Pharmacology
- Environmental Toxicology
- Analytical Chemistry
Background:
- Metformin is a common human diabetes medication with limited veterinary use.
- Adverse analytical findings of metformin in racehorse samples have recently emerged.
- Metformin is excreted unchanged in urine and is environmentally persistent, suggesting contamination risks.
Purpose of the Study:
- To investigate the potential for metformin exposure in horses via environmental contamination.
- To determine metformin absorption and excretion following exposure to contaminated bedding.
- To assess the implications of contamination for regulatory testing in racehorses.
Main Methods:
- Six horses were exposed to shavings contaminated with metformin-positive urine at varying concentrations (10, 135, 270 μg/mL).
- Blood (plasma, serum, whole blood, red blood cells) and urine samples were collected over 168 hours post-exposure.
- Metformin concentrations were determined using analytical methods.
Main Results:
- All horses exhibited detectable metformin concentrations in blood samples at least once during the study period.
- Metformin concentrations in urine were significantly higher than in blood.
- Metformin was detectable in urine as early as 4 hours post-contamination.
Conclusions:
- Environmental contamination with metformin is a plausible route of exposure for racehorses.
- The detection of metformin in biological samples should consider potential contamination, especially in racetrack environments.
- Regulatory strategies for metformin in racehorses need to account for exposure via contamination.
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