Aim: An approach of forced degradation study was successfully applied for development and validation of stability indicating assay method for the simultaneous estimation and quantification of three anti-hypertensive drugs, viz., Olmesartan Medoxomil, Hydrochlorothiazide and Amlodipine Besylate in marketed formulation in presence of its degradation products. The method showed adequate separation of all three drugs from their associated degradation products. Materials and Methods: The separation was achieved on Hypersil BDS C18 column (250 x 4.6 mm id, 5 �µm particle size) using mobile phase of triethylamine buffer solution (at pH 3): acetonitrile (gradient program). The flow rate was 1 ml/min and detection was done at 236 nm on photodiode array detector. Comprehensive stress testing of all drugs was carried out according to the International Conference on Harmonization (ICH) guideline Q1A (R2). The drug was subjected to acid hydrolysis, base hydrolysis, oxidation, dry heat, and photolysis to apply stress conditions. There were no other coeluting, interfering peaks from excipients, impurities, or degradation products due to variable stress conditions, and the method was specific for determination of all drugs in the presence of degradation products. The specificity of the method was determined by assessing interference from the placebo and by stress testing of the drug Results: The retention time for Hydrochlorothiazide, Amlodipine besylate and Olmesartan medoxomil was 3.7 min, 7.0 min and 8.4 min respectively. The linearity of method was investigated in range of 20-60 �µg/ml (r2=0.9999) for Olmesartan medoxomil, 12.5-37.5 �µg/ml (r2=0.9998) for Hydrochlorothiazide and 5-15 �µg/ml (r2=0.9998) for Amlodipine besylate respectively. Validation results indicated that method shows satisfactory linearity, accuracy, precision, robustness and ruggedness. Conclusion: Degradation products produced in stress studies did not interfere with the detection of main drugs and henceforth this stability indicating method can also be successfully employed for simultaneous estimation of all drugs in commercial products.
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