STEREOSELECTIVE HPLC BIOANALYSIS OF ATENOLOL ENANTIOMERS IN PLASMA - APPLICATION TO A COMPARATIVE HUMAN PHARMACOKINETIC STUDY

An enantioselective HPLC bioassay has been developed relying on extraction of (R)- and (S)-atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1-butanol followed by an achiral derivatization of the drug with phosgene leading to (R)- and (S)-oxazolidine-2-one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)-diaminocyclohexane-dinitrobenzoyl chiral stationary phase [(R,R)-DACH-DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0. 5 ng for (R)- and 0. 6 ng for (S)-atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross-over, double-blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)-, 50 mg (R)-, and 50 mg (S)-atenolol. AUC0-24 and C(max) values of (R)-atenolol were slightly but significant higher than those of (S)-atenolol. The R/S ratios were 1.09 for AUC(R)/AUC (S) and 1.03 for C(max) (R)/C(max)(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no differences between AUC, C(max), and t1/2 values of each enantiomer, whether they were administered as single enantiometers or in the form of its racemic mixture. (C) 1993 Wiley-Liss, Inc.