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.

High-performance liquid chromatographic assay for azatadine in human urine.

A high-performance liquid chromatographic assay for the quantitative determination of azatadine and a base (1 M sodium hydroxide) hydrolyzable conjugate of azatadine in human urine has been developed. Reversed-phase separation of azatadine and the internal standard, 8-chloroazatadine, was accomplished on a 300 X 3.9 mm I.D. mu Bondapak CN column. Following liquid-liquid extraction from urine, azatadine was quantitatively determined by UV detection at 214 nm. No interferences were observed in the extracts obtained from drug-free urine. Detector response (peak area ratio) was linear from 10 to 2500 ng/ml. This method has been shown to provide accurate and precise determinations of the unchanged and hydrolyzed drug in human urine, following the twice daily oral administration (1-2 mg) of azatadine maleate.

High-performance liquid chromatographic method for the determination of trace amounts of acetaminophen in plasma.

A method is described for the rapid, sensitive, and precise quantitation of acetaminophen in human plasma. The assay involved a single acetonitrile extraction and high-performance liquid chromatographic analysis using a reverse-phase column, with a mobile phase of methanol and water. The limit of quantitation of acetaminophen by this method was 8 ng/mL; only 0.1 mL of the plasma sample was required for the determination. N-Propionyl-p-aminophenol was used as the internal standard.