Simultaneous HPLC analysis of olmesartan and hydrochlorothiazide in combined tablets and in vitro dissolution studies

A simple, rapid and reproducible HPLC method was developed and validated for the simultaneous determination of olmesartan (OLM) medoxomil and hydrochlorothiazide (HCT) in combined tablets. Chromatography was carried outon a 4.6 mm LD x 200 mm, 5 pm cyanocolumn with methanol-10 mM phosphoric acid containing 0.1 % triethylamine (pH 2.5, 50:50 v/v) at a flow rate of 1.0 mL min(-1) and UV detector was set at 260 nm. Valsartan (VAL) was used as internal standard (IS). A linear response was observed in the range of 0.2-6 mu g mL(-1) (r(2) = 0.9998) for OLM and 0.1-4 pg mL(-1) (r(2) = 0.9999) for HCT, respectively. The method showed good recoveries (99.56% for OLM and 99.48% for HCT) and the relative standard deviation (RSD) values for intra- and inter-day precision were 0.70-1.59 and 0.80-2.00% for OLM and 1.20-1.37 and 1.63-1.93% for HCT, respectively. The developed method was applied successfully for quality control assay of OLM and HCT in combined tablets and in vitro dissolution studies.