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Abstract

A simple and sensitive Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry method was developed to perform a stability study of diltiazem and its metabolites in human plasma using various buffer reagents at a different strength. The method was applied for the quantification of diltiazem and its two major metabolites N-desmethyl diltiazem and desacetyl diltiazem in human plasma. The analytes were separated using a binary solvent delivery mode on a reversed-phase column and analyzed by Mass Spectrometry in the multiple reaction monitoring mode using the respective (M+H) + ions, m/z 415.05/178.03 for diltiazem, m/z 401.09/150.04 for N-desmethyl diltiazem m/z 373.21/108.85 for desacetyl diltiazem, m/z 419.22/314.0 for diltiazem-D4 (internal standard). The linearity was 0.93 to 250.10 ng/mL for diltiazem, 0.24 to 64.00 ng/mL for N-desmethyl diltiazem and 0.15 to 40.69 ng/mL for desacetyl diltiazem in human plasma. The lower limit of quantification was 0.93 ng/mL, 0.24 ng/mL and 0.15 ng/mL for diltiazem, N-desmethyl diltiazem, and desacetyl diltiazem, respectively. The plasma samples buffered with 1% of 0.1 M NaF solution was able to limit the degradation of diltiazem to desacetyl diltiazem for longer storage periods at-70 °C. INTRODUCTION: Diltiazem hydrochloride (2S, 3S)-5-(2-(dimethylamino) ethyl)-2-(4-methoxy phenyl)-4-oxo-2, 3, 4, 5-tetrahydro benzo [b][1,4] thiazepine-3-yl acetate hydrochloride is a calcium channel blockers indicated not only in the treatment of classical and vasospastic angina pectoris but also in the treatment of supraventricular tachyarrhythmia and essential hypertension. Diltiazem (DTZ) is metabolized by N-demethylation, O-demethylation, and deacetylation 1 .