Clenbuterol and the Horse

Clenbuterol is a b2-agonist bronchodilator and mucokinetic drug. When administered at the recommended dose of 0.8 mg/kg q 12 h, it reaches plasma levels that should relax airway smooth muscle. However, the measurable degree of bronchodilation achieved may not always be clinically obvious even in horses with heaves. After a ten-day treatment (0.8 mg/kg q 12 h), the half-life of elimination from plasma is about ten hours and plasma levels are below the pharmacological threshold within three days. Urinary elimination is prolonged and irregular so that control of clenbuterol usage in racehorses should be based on blood rather than urine levels. Author’s address: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824-1314. © 2000 AAEP.