Stability indicating LC method for the simultaneous determination of amlodipine and olmesartan in dosage form.

A simple, rapid, and precise method is developed for the quantitative simultaneous estimation of amlodipine (AM) and olmesartan (OL) in combined pharmaceutical dosage form. A chromatographic separation of the two drugs was achieved with an ACE 5 C(18) 25-cm analytical column using buffer-acetonitrile (60:40, v/v). The resolution between OL and AM was found to be more than 12. Theoretical plates for OL and AM were 6970 and 11,841, respectively. Tailing factor for OL and AM was 0.90 and 0.98, respectively. OL, AM, and combination drug product were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Peak homogeneity data of OL and AM is obtained by photodiode array detector in the stressed sample chromatograms, demonstrating the specificity of the method for their estimation in presence of degradation product. The described method shows excellent linearity over a range of 20-400 microg/mL for OL and 5-100 microg/mL for AM. The correlation coefficient for OL and AM are 0.9995 and 0.9998, respectively. The relative standard deviation for six measurements in two sets of each drug in tablets is always less than 2%. The proposed method was found to be suitable and accurate for quantitative determination and stability study of OL and AM in pharmaceutical preparations.