An ion-pair reverse phase high performance liquid chrofflatograph method wasdeveloped for simultaneuosly estimating metoprolol and its metabolite a-hydroxy-metoprolol in human plasma

saliva and urine. The extraction efficiency was above 90% in urine for both compounds. This assay procedure was reproducible and precise for metoprolol and a-hydroxymetoprolol

as judged by the coefficient of va-riation<6.4% on inter-day and intra-day determinates at all concontrarions examined. The minimum detection limit of metoprolol was 10 ng/ml in plasma

saliva and urines and that of a-hydroxymetoprolol was 50 ng/ml in plasma and 10 ng/ml in saliva and urine. The calibration curves over the range of 0.1-10 ug/ml for both compounds had high linear relationship and reproducibility

either by external standard method or internal standard method

using propranolol as the internal standard