High Pressure Liquid Chromatography of Labetalol in Serum or Plasma

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Abstract
A sensitive method for monitoring serum or plasma labetalol (2-hydroxy-5-[1-hydroxy-2-(1-methyl-3-phenylpropylamino) ethyl] benzamide hydrochloride), a combined .gamma.- and .beta.-adrenoceptor antagonist used in the treatment of hypertension, is described. The method is designed to study single dose kinetics and assess predose labetalol levels during chronic treatment. The applicable range of the assay is 10-400 ng/ml using 1 ml of plasma or serum. The method uses reverse-phase high pressure liquid chromatography (HPLC), a mobile phase of acetonitrile/pH 3.0 phosphate and UV detection at 207 nm. The percentage recovery of labetalol and the internal standard, propericiazine (3-cyano-10-[3-4-hydroxypiperidino) propyl] phenothiazine, from serum was 95.6% and 75.5%, respectively. The precision of the method at labetalol serum concentrations of 400 and 50 ng/ml was indicated by a coefficient of variation of 4.3% and 6.9%, respectively. An approximate 4-fold variation in plasma labetalol concentration, with plasma levels ranging from 20-93 ng/ml, was seen 10-11 h after a dose in a group of patients taking 200 mg twice per day.

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