High-performance liquid chromatography with ultraviolet and fluorimetric detection for the simultaneous determination of tacrine, nimodipine, and their respective metabolites in the plasma of patients with Alzheimer disease.

A new high-performance liquid chromatography (HPLC) assay was developed for the simultaneous determination of tacrine (THA), nimodipine, and their three metabolites (MI, MII, and MIII) using a 1-ml plasma sample volume. A liquid-liquid extraction procedure was coupled with a reverse-phase HPLC separation. Quantification was performed by fluorometric detection for THA and metabolites and by ultraviolet detection for nimodipine and metabolites. Peak-height ratios were linear across the ranges 0.5 to 100 micro/l for THA and its three metabolites; 2 to 500 microg/l for nimodipine, MII, and MIII; and 4 to 500 microg/l for MI. Correlation coefficients were better than 0.998 for all compounds. Accuracy and precision were less than 12% for the entire concentration range for each substance. This method is sensitive and selective. Analysis of plasma samples collected from patients with Alzheimer disease demonstrated that the assay is suitable for clinical and pharmacokinetic trials including drug-drug interactions studies.