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.
Supported by a grant from the Kentucky Equine Drug Research Fund.
Combie, Joan; Nugent, Thomas E.; and Tobin, Thomas, "Pharmacokinetics and protein binding of morphine in horses" (1983). Maxwell H. Gluck Equine Research Center Faculty Publications. 92.