Determination of Hydrochlorothiazide and Enalapril Maleate in Tablet Formulations by Reversed-Phase HPLC

Hydrochlorothiazide (HCT) is a thiazide diuretic which reduces the resorption of electrolytes and consequently of water. Enalapril maleate (EM) is a derivative of 2 amino acids, L-alanine and L-proline, and is an antihypertensive and a vasodilator in congestive heart failure. The 2 drugs are used in association in the treatment of hypertension . Several methods are available in the literature for the determination of HCT and EM. Most of these methods are for the determination of either HCT or EM separately. For instance, HCT has been determined in urine samples and tablet formulation by HPLC2−3 and by non-aqueous titration. Enalapril maleate has been analyzed in pharmaceutical combinations containing 0.5-0.1% methylcellulose by extraction to acetonitrile and injecting the extracts to HPLC. However, few methods are present in the literature for the simultaneous determination of EM and HCT. Enalapril maleate and HCT were determined simultaneously in pharmaceutical tablets using first-derivative ultraviolet spectrophotometry, with zero-crossing and peak-tobase measurement methods and by HPLC with either programmable UV-detectors at 2 different wavelengths or with electrochemical detection6−7. In many cases, the direct UV/VIS methods lack specificity, because many compounds my absorb in the UV region and they will interfere if they are not separated. Other methods described in the literature6−7 are based upon the use of either a programmable UV-detector or