High-performance liquid chromatographic assay for dilevalol in human plasma and urine using a PRP-1 column and fluorimetric detection

A single high-performance liquid chromatographic (HPLC) assay for the quantitative determination of dilevalol, the R,R isomer of labetalol, was developed for both plasma and urine. A significantly improved limit of detection for dilevalol in plasma was accomplished by extensive modification of an HPLC assay originally developed in our laboratory for labetalol. This simplified method is readily adaptable to urine and represents the first reported HPLC assay for the quantitative determination of dilevalol in this biofluid. Drug was recovered from plasma or urine by partition into diethyl ether under mildly alkaline conditions and back-extraction into dilute acid. Reversed-phase separation of dilevalol and the internal standard was accomplished on a 150 X 4.1 mm column commercially packed with a spherical (5 micron) macroporous copolymer (PRP-1). No interferences were observed in extracts obtained from drug-free plasma or urine. Selectivity for dilevalol in the presence of other beta-blockers was established. This method demonstrated a linear detector response to concentrations of unchanged drug typically observed in urine and plasma following once-a-day treatment with dilevalol hydrochloride (100-800 mg). The lowest limit of reliable quantitation was established at 1 ng/ml in plasma. The intra-assay precision (coefficient of variation) remained less than 6% at all concentrations evaluated from 1 to 800 ng/ml. In urine, the lowest limit of quantitation was validated to 20 ng/ml where the intra-assay precision (coefficient of variation) for unchanged drug was less than 4% at all concentrations evaluated up to 400 ng/ml. This method is suitable for routine quantitation of unchanged drug in human plasma and urine following the administration of therapeutically effective doses of dilevalol hydrochloride.