Caffiene, theophylline and theobromine are naturally occurring members of the methylxanthine family;pentoxfylline, dyphylline and enprofylline are structurally related synthetic pharmaceuticals. Caffiene has predominantly central nervous system effects, theophylline, dyphylline and enprofylline have predominantly bronchodilator effects, while theobromine is associated with diuretic responses. Pentoxfylline is thought to increase red cell deformability and facillitate blood flow through capillary beds. The methylxanthines are not highly potent agents; they are typically administered in gram doses and they tend to have relatively long half-lives. They remain detectable in plasma and urine for relatively long periods. Similarly, traces of the naturally occurring members of this family are not uncommonly identified in forensic samples. In this review we report on the detection, actions, uses and regulatory control of this group of agents in performance horses.

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Published as No. 211 from the Equine Pharmacology and Experimental Therapeutics Program at the Maxwell H. Gluck Equine Research Center and the Department of Veterinary Science, University of Kentucky. Published as Kentucky Agricultural Experiment Station Article No. 96-14-084 with the approval of the Dean and Director, College of Agriculture and Kentucky Agricultural Experiment Station. Supported by grants from the Kentucky Racing Commission and the Kentucky Equine Drug Council, Lexington, KY, the National and Florida offices of the Horsemen's Benevolent and Protective Association, Aventura, FL, the Grayson­Jockey Club Research Foundation, Lexington, KY and Mrs. John Hay Whitney and The American Feed Industry Association.