LABETALOL ANALYSIS IN HUMAN-PLASMA USING LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION - APPLICATION TO PHARMACOKINETIC STUDIES

Labetalol determination in human plasma by a sensitive (to 2.5 ng/ml) and selective method using liquid chromatography with electrochemical detection is described. Plasma is extracted with diethyl ether under mildly basic (pH 9) conditions, back-extracted into an aqueous acidic buffer, then injected directly on column. Standard curves using propranolol as an internal standard are linear for concentrations from 2.5 to 200 ng/ml. Within-day and between-day reproducibility is satisfactory with coefficient of variation less than 8% for all concentrations. Sample recovery from the extraction is complete at all concentrations. Utility of the method is demonstrated by a pharmacokinetic study in a hypertensive volunteer who received 43.75 mg labetalol by 10 minute intravenous infusion.