Determination of nadolol diastereomers in dog plasma using chiral derivatization and reversed-phase high-performance liquid chromatography with fluorescence detection

A stereospecific high-performance liquid chromatographic method has been developed for the determination of four diastereomers of nadolol in plasma. After the nadolol diastereomers were extracted from plasma using an Extrelut-1 solid-phase extraction cartridge, they were derivatized with (R)-(-)-1-(1-naphthyl)ethylisocyanate to form urea derivatives. These derivatives were then separated on a YMC-AM-303 ODS column using water-acetonitrile (60:40, v/v). The calibration curves of (SR)-, (RS)-, (SS)-, and (RR)-nadolol were linear over the range 2.5-200 ng/ml, and the correlation coefficient (r) of the curves were higher than 0.9991 for each diastereomer. The limit of quantification was 2.5 ng/ml for each diastereomer in plasma. This method was used for a pharmacokinetic study in four dogs after oral administration of nadolol (1 mg/kg). The plasma concentrations of nadolol diastereomers showed no significant differences in Cmax, Tmax or AUC values. The assay appears to be readily applicable to the study of diastereoselective nadolol pharmacokinetics in animals and humans.