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)‐diaminocylohexane‐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 Cmax 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 Cmax (R)/Cmax(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no differences between AUC, Cmax, and t½ values of each enantiomer, whether they were administered as single enantiometers or in the form of its racemic mixture. © 1993 Wiley‐Liss, Inc.