The pharmacokinetics and pharmacodynamics of a betamethasone (formulation dipropionate and sodium phosphate) were evaluated in 4 healthy camels after a single intramuscular dose of 35 μg/kg body weight. A sensitive, validated LC-MS/MS method for the quantification of plasma betamethasone and hydrocortisone was developed. Plasma betamethasone versus time concentration was best described by a two-compartment open model. The pharmacokinetic parameters median and range were as follows: terminal elimination half-life was 7.17 (6.93-7.58) h, Cmax was 15.9 (10.8-20.85) ng/ml, and Tmax was 0.5 (0.25-0.75) h. The estimated IC50 for hydrocortisone (mean ± SD) was 0.09 ± 0.08 ng/ml. Based on the analytical method and plasma terminal elimination half-life, a 4-day withdrawal period of the betamethasone formulation is advised prior to racing.
Key words: Betamethasone, camels, pharmacokinetics, pharmacodynamics