PHARMACOKINETICS OF PHENYLBUTAZONE IN CAMELS

Objective-To document disposition variables of phenylbutazone and its metabolite, oxyphenbutazone, in camels (Camelus dromedarius) after sin gle IV bolus administration of phenylbutazone, with a view to making r ecommendation on avoiding violative residues in racing camels. Animals -6 healthy camels (4 males, 2 females), 5 to 7 years old, and weighing from 350 to 450 kg. Procedure-Blood samples were collected at 0, 5, 1 0, 15, 45, and 60 minutes and at 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 12, 24, 26, 28, 30, 40, 48, 50, 53, and 60 hours after IV administration o f 4.5 mg of phenylbutazone per kg of body weight. Urine was obtained i n fractions during the entire blood sample collection period. Serum an d urine phenylbutazone concentrations were measured by high-performanc e liquid chromatography; assay sensitivity was 100 ng/ml. Serum oxyphe nbutazone concentration was measured by gas chromatography/mass spectr ometry; assay sensitivity was 70 ng/ml. Results-Disposition of phenylb utazone was best described by a two-compartment open model. Mean +/- S EM elimination half-life was 13.44 +/- 0.44 hours. Total body clearanc e was 12.63 +/- 1.64 mg/kg/h. Renal clearance was between 0.3 and 0.4% of total body clearance. The elimination half-life of oxyphenbutazone was 23.9 +/- 2.09 hours. Conclusions-The elimination half-life and to tal body clearance of phenylbutazone in camels are intermediate betwee n reported values in horses and cattle. Extrapolation of a dosage regi men from either species to camels is, therefore, not appropriate. Elim ination of phenylbutazone in camels is mainly via metabolism. Owing to the long half-life of phenylbutazone and of oxyphenbutazone, and to t he zero drug concentration regulation adopted by the racing commission er in the United Arab Emirates, practicing veterinarians would be advi sed not to use phenylbutazone in camels for at least 7 days prior to r acing.