HPLC Quantification of Diltiazem in Plasma from Man

A rapid, simple and sensitive reversed-phase HPLC method has been developed for quantification of diltiazem in plasma. The assay enables the measurement of diltiazem for therapeutic drug monitoring with a minimum detectable limit of 2 ng mL−1. The method involves simple, one-step solvent extraction of the drug with 50:50 (v/v) n-hexane-ether then HPLC on an analytical C18 column with 35:35:30:0.05 ammonium chloride (0.04M)-methanol-acetonitrile-triethylamine, adjusted to pH6.3, as isocratic mobile phase. Diltiazem was monitored by ultra-violet detection at 237 nm. The calibration curve was linear over the concentration range 8–200 ng mL−1 and average recovery was 90±5.3% over the concentration range 50–300 ng mL−1. The coefficients of variation for inter-day and intra-day assay were within the range of clinical usefulness.