Simultaneous determination of nitrendipine and one of its metabolites in plasma samples by gas chromatography with electron-capture detection

Validated LC-MS/MS method for the simultaneous determination of enalapril maleate, nitrendipine, hydrochlorothiazide, and their major metabolites in human plasma

Hypertension is a major risk factor for atherosclerosis and ischemic heart disease. Most hypertensive patients need a combination of antihypertensive agents to achieve therapeutic goals. A rapid, sensitive, and selective liquid chromatography-tandem mass spectrometric method was developed and validated for simultaneous determination of enalapril maleate (ENA) and its major metabolite enalaprilat (ENAT), nitrendipine (NIT) and its major metabolite dehydronitrendipine (DNIT), and hydrochlorothiazide (HCT) in human plasma using felodipine as an internal standard (IS). The drugs were extracted from plasma using one-step protein precipitation. Chromatographic separation was performed on a Symmetry C₁₈ column, with water and acetonitrile (10:90, v/v) as mobile phase. The detection was carried out using multiple reaction monitoring mode and coupled with electrospray ionization source. Multiple reaction monitoring transitions were m/z 377.1 → 234.1 for ENA, m/z 349.2 → 206.1 for ENAT, m/z 361.2 → 315.1 for NIT, m/z 359 → 331 for DNIT, m/z 295.9 → 205.1 for HCT, and m/z 384.1 → 338 for felodipine (IS). The method was linear over concentration ranges of 1-200, 20-500, 5-200, 2-100, and 5-200 ng/mL for ENA, ENAT, NIT, DNIT, and HCT, respectively, with r² ≥ 0.99. Method validation was performed according to U.S. Food and Drug Administration guidelines. The validated method showed good sensitivity and selectivity and could be applied for therapeutic drug monitoring and bioequivalence studies.

Development of a LC-ESI-MS3 method for determination of nitrendipine in human plasma

A novel and sensitive method utilizing high performance liquid chromatography coupled with electrospray ionization source tandem mass spectrometry (LC-ESI-MS(3)) was developed for the first time in order to analyze nitrendipine in human plasma samples. Human plasma samples were prepared by protein precipitation with acetonitrile and well resolved on a 100 mm reversed-phase column in gradient elution with 0.05% (v/v) formic acid in acetonitrile as the mobile phase. Determination was performed in MS(3) scan mode for nitrendipine and in the multiple reaction monitoring (MRM) mode for nimodipine (internal standard). This method, having a lower limit of quantification (LLOQ) of 0.05 ng/mL when using a 100 μL sample aliquot (5 pg/sample), is acceptable for calibration of the linearity and repeatability and is of better sensitivity than the reported methods (>0.25 ng/mL). The major advantages of the method are that small sample volume (100 μL) is required, simple sample processing technique, high sensitivity and excellent selectivity is guaranteed by the MS(3) detection. The proposed validated method has been successfully applied to a clinical study on nitrendipine.