A new minimum reporting level (MRL) for the banned substance metformin has been proposed by HISA's Anti-Doping and Medication Control (ADMC) Committee, according to a HISA release Monday. The proposed MRL is 4.0 nanograms per milliliter in blood and is based on recommendations received at HISA and HIWU's request from the Racing Medication & Testing Consortium's (RMTC) Scientific Advisory Committee (SAC). The modification will be circulated for public comment in the coming days.
Following a series of positive test results for metformin and what Monday's HISA release called, “intelligence received by HIWU that trainers were intentionally administering metformin to Covered Horses to enhance performance,” HISA and HIWU called for an independent review of the available science relating to metformin by the RMTC's SAC in June 2024 to determine if it was appropriate to modify the regulation of this substance. During the review, HIWU stayed the prosecution of all unresolved and new cases involving potential positive tests for metformin, although there have been zero reported AAFs in 2025 while testing at 0.5 nanograms per milliliter in blood and 1 nanogram per milliliter in urine.
After the review, which consisted of a study of existing scientific literature followed by a three-part study performed by Dr. Heather Knych with the K.L. Maddy Equine Analytical Chemistry Laboratory at the University of California (UC), Davis School of Veterinary Medicine, the SAC agreed that an MRL of 4.0 nanograms per milliliter in blood reflects exposure to metformin due to intentional administration and minimizes the possibility of a reported AAF due to inadvertent exposure.
Dr. Knych's administration study determined that metformin demonstrates an erratic elimination behavior in urine and an inconsistent relationship between urine and blood concentrations. Therefore, the SAC recommended that laboratories perform confirmatory analysis in blood only.
“We are thankful to UC Davis, Dr. Knych, and her team for performing ground-breaking research on metformin. HISA and HIWU's call for this review of metformin aligns with our mandate to utilize science when making regulatory decisions to prioritize safety, integrity, welfare, and fairness,” said HIWU Executive Director Ben Mosier. “Additionally, we appreciate our ongoing collaboration with the RMTC's SAC to facilitate these research projects and ultimately enhance the effectiveness of the ADMC Program.”
There are currently nine unresolved (and therefore stayed) presence cases for metformin, which, according to the HISA release, will continue to be stayed pending the Federal Trade Commission's approval of the new MRL. If the new MRL is approved, it will not impact cases that were resolved prior June 2024 and involved violations of the rules and testing specifications in effect at the time.
TDN reached out to HISA for clarification on how the unresolved cases would be impacted if the new MRL was adopted and whether those cases involved positives above or below the newly proposed threshold. HISA responded via email, “HIWU cannot disclose the reported levels of metformin for the currently stayed cases. If the FTC approves the proposed Minimum Reporting Level, cases below the new MRL will be withdrawn at that time and updated on the HIWU website. Stayed cases that are not affected by the proposed MRL will continue through the adjudication process upon the FTC's approval of the rules, and their status will be updated on the HIWU website once resolved.”
While nine positive results were returned after the June announcement of the RMTC study of metformin levels, there were seven that occurred before HISA and HIWU began staying any unresolved and new cases. Of these seven prior cases, two were withdrawn due to a harmonized testing specification, one was withdrawn when the B Sample could not be confirmed due to low sample volume, and the remaining four were resolved through either admissions or arbitration, according to a HIWU spokesperson. According to the HIWU spokesperson, all of those seven prior cases were under the new proposed Minimum Reporting Level in blood.
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