The results of the “Clenbuterol plasma concentrations after therapeutic administration in fit Standardbred horses: threshold recommendations” study published online after peer review in Comparative Exercise Physiology clearly demonstrate and recommend the need for different withdrawal times and threshold levels for harness racing than the current standards that exist for Thoroughbred and Quarter Horse racing.

The goal of this study was to identify a withdrawal time guideline for use of clenbuterol at dose levels approved by the United States Food and Drug Administration (FDA) in harness racing, where horses may start (race) at seven-day intervals.

Three members of the Harness Racing Medication Collaborative — Kenneth McKeever, PhD FACSM; George Maylin, DVM, MS, PhD; and Clara Fenger DVM, PhD, DACVIM — collaborated on the study.

“The results of this study once again demonstrate the need for different therapeutic medication rules for different breeds due to the differences in their racing and training models,” said United States Trotting Association chairman Joe Faraldo, who also serves as chairman of the Harness Racing Medication Collaborative.

“For Quarter Horses, the zero tolerance use of clenbuterol is supported because of recognized abuse via the sequence of daily and prolonged administration of the medication,” said Faraldo, based upon previous studies cited. “The Thoroughbred rule at 140 pg/mL in urine at a 14-day withdrawal period also seems appropriate because of the manner of the use of clenbuterol leading up to race day.

“But this peer-reviewed and published study definitively concludes that in the harness performance model, a 96-hour withdrawal time and a threshold level of 41 pg/mL in plasma fits that model of almost weekly racing without any erosion of integrity.

“Imposing a 14-day withdrawal and 140 pg/mL on the harness racing model is just scientifically disputed because the dosage and method of administration of clenbuterol as indicated in this study does not have a muscle building effect and is within the FDA and the manufacturer’s prescribed usage.”

To read the complete study, click here.

The highlights of the study include:

• Data from the results show that a 41 pg/mL plasma threshold for clenbuterol is a practical threshold to regulate the use of three-day, twice daily (BID) 0.8 μg/kg administration protocol for clenbuterol in racing Standardbred horses, where the horse may be racing again 96 hours after the last administration.

• There were no effects of clenbuterol on body composition on any of the measures including fat mass and fat free mass and thus no repartitioning effect was observed, consistent with the effects of this therapeutic administration schedule being limited to the respiratory system.

• Clenbuterol is an FDA-approved therapeutic medication used for the management of Inflammatory Airway Disease and airway obstruction in horses. Because IAD commonly affects racehorses in training, the use of clenbuterol is appropriate.

• Administration above the FDA approved doses of clenbuterol produces repartitioning effects, which have led to restriction on its use in human athletes and Quarter Horse and Thoroughbred racing. Clenbuterol, however, has long been used therapeutically at FDA approved doses in harness racing.

• Eight healthy, moderately fit Standardbred horses (four mares, four geldings, weight 491 +/-40 kg, age 13 +/-two years) were administered 0.8 μg/kg of clenbuterol as Ventipulmin syrup twice daily (BID) for three days. Blood samples were collected prior to dosing and at 1, 24, 48 and 96 hours post administration. One horse developed gastrointestinal illness and was excluded from the results.

The USTA will distribute the results of this study to the Association of Racing Commissioners International with the recommendation to adopt the proposed withdrawal time and threshold level for harness racing in their model rules and to all appropriate racing commissions for adoption in their state rules regulating the use of clenbuterol.

(USTA)