Simultaneous determination of enalapril maleate and nitrendipine in tablets using spectrophotometric methods manipulating ratio spectra.

A fixed dose combination of enalapril maleate (EN) and nitrendipine (NT) achieved satisfactory blood pressure control rather than monotherapy. Four accurate spectrophotometric methods utilizing ratio spectra were developed and validated for the simultaneous determination of EN and NT in combined pharmaceutical dosage form (Eneas® tablets). The first method was first derivative ratio spectrophotometric method (1DD) where the amplitudes maxima were measured at 219.2 nm and 233.4 nm for the determination of EN and NT, respectively. The second method was ratio difference spectrophotometric method where EN and NT were estimated by measuring the amplitudes difference between 213 nm and 225 nm on the ratio spectrum of EN and between 241 nm and 227 nm on the ratio spectrum of NT. The third method was ratio subtraction followed by extended ratio subtraction, EN was determined at 210 nm by subtraction of the constant values from the ratio spectrum then multiplication with the divisor (NT spectrum). An extended ratio subtraction method was then applied in order to determine NT at 235 nm by using the zero-order spectrum of EN (10 µg/ml) as a divisor. The fourth method was ratio subtraction coupled with constant multiplication methods. The zero- order absorption spectrum of the laboratory prepared mixture was divided by NT (12 µg/ml) spectrum, subsequently, the value of the constant was multiplied by the divisor to obtain the original spectrum of NT, followed by its subtraction from the laboratory prepared mixture to get the spectrum of EN. EN and NT were determined at 210 nm and 235 nm, respectively. Linearity was ascertained over the concentration ranges of (1-11 µg/ml) for EN and (2-14 µg/ml) for NT, for the first and second methods and (2-13 µg/ml) for EN and (3-20 µg/ml) of NT, for the third and fourth methods. Application of the methods to the determination of the cited drugs in Eneas® tablets gave satisfactory results. Methods validation confirmed their accuracy and selectivity. Statistical comparison of the results with the reported one showed no significant difference, regarding precision and accuracy. Routine analysis of the cited drugs in quality control laboratories could be performed using the developed methods.

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.