Direct assay of conjugates of penbutolol and its metabolites in urine.

The metabolites of 1-tert.-butylamino-3-(2-cyclopentylphenoxy)propan-2-ol (penbutolol, Betapressin), penbutolol 2-glucuronide, 4'-OH-penbutolol 2-glucuronide, 4'-OH-penbutolol 4-sulfate and 1"-dehydropenbutolol 2-glucuronide were determined in urine by high-performance liquid chromatography (HPLC). The compounds were determined after direct injection, that is to say without prior cleavage of the conjugates to the corresponding aglycones. In the case of the glucuronides, the urine was injected into the HPLC system without further sample preparation. The sulfate was determined after ion-pair extraction. Fluorimetric detection was employed. Depending on the compound, the detection limits lay between 0.07 and 0.3 micrograms/ml. This method was used to determine the cumulative urinary excretion of a subject.