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 C_max, T_max or AUC values. The assay appears to be readily applicable to the study of diastereoselective nadolol pharmacokinetics in animals and humans.