HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF PENBUTOLOL ENANTIOMERS IN PLASMA WITH FLUORESCENCE DETECTION

The simultaneous determination of (R)- and (S)-penbutolols in plasma by high-performance liquid chromatography (HPLC) with fluorescence detection is described. The penbutolol enantiomers were derivatized with a chiral axis reagent, (aS)-2'-methoxy-1,1'-binaphthalene-2-carbonyl cyanide, and the diastereomeric esters formed were resolved by HPLC on a normal-phase column employing 0.005% triethylamine in hexane/ethyl acetate (6:1, v/v) as a mobile phase. The combined use of a Sep-pak C18 cartridge and an ion-exchange gel, carboxymethyl Sephadex LH-20, was effective for efficient cleaning of penbutolol in plasma. The enantiomeric drugs spiked to the plasma were recovered at a rate of over 96% with satisfactory reproducibility. The quantitation limit of each enantiomer was 500 pg/ml. The plasma-level profile of penbutolol enantiomers in a dog administered with the racemate was investigated by the newly developed method.