[Comparison of the pharmacokinetic profiles of clenbuterol in rat and dog during toxicological studies (author's transl)]

Abstract

The pharmacokinetics of the beta-sympathomimetic 4-amino-alpha-[(tert.-butylamino)methyl]-3,5-dichlorobenzyl alcohol hydrochloride (clenbuterol, NAB 365) have been investigated in two animal species during the chronic toxicological studies after single and multiple dosing. After oral administration of 2.5 mg/kg (dog) and 5 mg/kg (rat) the plasma levels showed significant differences. Moreover, a marked sex difference was to be seen in the plasma levels of the rat. The excretion, established only in the dog, showed no difference after single or multiple administration. The elimination occurs predominantly via the kidneys, and the main urinary elimination product is the unchanged clenbuterol. Each of the 8 metabolites is formed only in minor quantities. The biotransformation is not altered by long-term administration. The differences in the plasma levels that are observed with larger doses can be explained by the biological adaptation of the gastrointestinal tract during multiple administration.