METABOLIC-FATE OF CLENBUTEROL IN CALVES

The metabolic fate of [C-14]clenbuterol was studied in two calves, fol lowing single or repeated oral administration of the drug at an anabol ic dosage (5 mu g/kg). Analytical methods were developed to evidence t he nature of clenbuterol's metabolites in excreta and tissues. The maj or biotransformation pathways of clenbuterol were 4-N-oxidation, 4-N-s ulfation, and oxidative N-dealkylation of the parent compound. Unchang ed clenbuterol accounted for about 20 and 50% of the radioactivity det ected in urine and feces, respectively, and for a very large part of t he radioactivity detected in organs ( greater than or equal to 90%). R etina extracts contained only clenbuterol. Two different extraction te chniques and the use of H-3-labeled clenbuterol hydroxylamine demonstr ated that this labile compound was not present in liver extracts. Ther efore, the toxicity of clenbuterol residues remaining in tissues of ca ttle treated with this P-agonist toward the consumer is expected to be solely related to unchanged clenbuterol. The implications of the pres ent results on the monitoring of illegal clenbuterol use in cattle, fo llowing detection in matrixes such as urine, liver, or retina are disc ussed.