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Simple novel spectrophotometric methods for the determination of two antihypertensive mixtures containing hydrochlorothiazide in pharmaceutical dosage forms

Maha Farouk, Omar Abd EL-Aziz, Marwa H.El-Taweel

Three simple, rapid, accurate and precise spectrophotometricmethods have been developed for the simultaneous determination of telmisartan/ hydrochlorothiazide and bisoprolol fumarate/ hydrochlorothiazide binary mixtures. The first is an isosbestic method for determination of telmisartan/ hydrochlorothiazide mixture in a concentration range of 2-40 ìg.ml-1 for both drugs. The absorbance of the zero order spectra at 266 nm(isosbestic point) was corresponding to the total concentration, while telmisartan was selectively determined from the amplitudes of the first derivative spectra (D1) at 323 nm. The second is a ratio subtraction method for bisoprolol fumarate determination in presence of hydrochlorothiazide by measuring the absorbance at 224.4 nmwhere hydrochlorothiazide (10 ìg.ml-1) used as a divisor. The linearity was achieved over concentration range of 2-30 ìg.ml-1. The third is a dual wavelength method for hydrochlorothiazide determination in presence of bisoprolol fumarate without any interference in a concentration range of 1-20 ìg.ml-1. This was performed bymeasuring the absorbances difference (ÄA) at 266 and 277.8 nm,where the absorbances values of bisoprolol fumarate were the same. The proposed methods have been validated as per ICH guideline and were found to be valid and suitable for the assay of the cited drugs in raw materials and combined dosage forms.