“I’ll give you my gun when you take it from my cold, dead hands” – Charlton Heston
The drug Clenbuterol is a β2 agonist with some structural and pharmacological similarities to epinephrine (adrenaline). Therapeutically, clenbuterol is a fantastic bronchodilator and has been approved by the FDA for use in horses for the management of airway obstruction. If a horse has mucus in the throat there is nothing better on the market that can clean it up and help the horse get to the racetrack.
That is the good.
Clenbuterol is also the drug that cyclist Alberto Contador of Spain was banned for two years from professional cycling after testing positive for at the 2010 Tour de France. It is the drug that former New York Mets clubhouse employee Kirk Radomski admitted in his plea deal to distributing to dozens of current and former Major League Baseball players and associates. This is the same drug that San Francisco Giants pitcher Guillermo Mota received a 50-game suspension (in 2006) and 100 games (in 2012) due a positive test for and it is the same drug that Mexican boxer Erik Morales was suspended for 2 years after testing positive for earlier this year.
In humans it causes an increase in aerobic capacity and oxygen transportation and it increases the rate at which body fat is metabolized while increasing the body’s resting metabolic rate. It’s a straight out performance enhancer. In racehorses, it has a wide range of effects:
- Kearns et, al (2001) found that chronic administration of clenbuterol has a repartitioning or steroidal effect. It was noteworthy that they found that chronic clenbuterol administration causes significant repartitioning in the horse, even when administered in therapeutic doses. Thus if you give the recommended dose, but use it frequently, you get a steroidal effect.
- McKeever et, al (2002) found that therapeutic levels of clenbuterol and training actually decrease aerobic performance and that the resultant reduction in plasma volume may also affect improvements in cardiovascular function during recovery normally seen with exercise training.
- McKeever, et al (2002) found in standardbreds that chronic clenbuterol administration may negatively alter cardiac function by altering the internal diameter, thickening the septal wall and increasing aortic root dimensions.
- Nolen-Walston, et al (2012) found that clenbuterol initially reduced airway sensitivity to inhaled histamine, but that prolonged administration of clenbuterol likely results in a reduction in its bronchodilatory effects. That is, if you abuse it, the horses system gets used to it and the drug is less effective in treating what it was meant to treat. Importantly in an interview on the paper Nolen-Walston added, ”Our study shows that after about two weeks of use, it quits working and actually makes the horses breathe a little bit worse. The clinical significance is that clenbuterol should be used for no more than 14 days consecutively without a break.”
- Finally McConnico, et al (2012) found in Quarter horses that clenbuterol doses ≥ 10 2μg/kg (4.5 μg/lb), in excess of those normally prescribed, may cause sustained tachycardia, muscle tremors, hyperglycemia, and cardiac and skeletal muscle necrosis.
Therein lies the problem.
As good a drug as it is, when it is abused its efficacy to treat what it is there to treat (airway obstruction) is diminished and steroidal and other negative effects emerge.
So why is clenbuterol regulation important?
In the last ten years there have been a number of cases where non-FDA approved compounded clenbuterol had resulted in horse deaths including six in Louisiana in 2006 and there had been for a considerable time horsemen’s belief that the drug was being abused beyond its therapeutic use for steroidal effect even before steroids were officially banned from racing in 2008/09. At a California Horse Racing Board meeting in 2007, equine medical director Dr Rick Arthur said that “recent blood tests the CHRB has been performing on horses racing in California indicate that only 14% of the horses showed any measurable levels of clenbuterol.”
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