Morphine could be detected in horses dosed with 0.1 mg of drug/kg of body weight for up to 48 hours in blood and 144 hours in urine. This dose of morphine elicited no observ­able effects and is a suggested an­algesic dose. Computer analysis revealed that a 3-compartment open system was the best fitting model with a serum half life of 87.9 minutes and a urine half life of 101.1 minutes. Binding to equine serum proteins was linear over a drug con­centration range of 3.88 x 10-5M to 3.50 x 10-aM and averaged 31.6%. In RBC-partitioning experiments, 78.1 % of the drug was found in the plasma fraction. The data indicated that a horse should not be given morphine closer than 1 week before a race.

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Published as Kentucky Agricultural Experi­ment Station article No. 81-4-255, College of Agri­culture and Kentucky Agricultural Experiment Station, with approval of the Dean and Director. Published as publication No. 76 from the Kentucky Equine Drug Research Program and Graduate Cen­ter for Toxicology, University of Kentucky.

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Supported by a grant from the Kentucky Equine Drug Research Fund.