DEVELOPMENT AND VALIDATION OF A HPLC/PDA METHOD FOR SIMULTANEOUS QUANTIFICATION OF AMLODIPINE BESYLATE AND VALSARTAN IN DISSOLUTION MEDIA

Abstract

Background: Valsartan, an angiotensin blocker, is often combined with amlodipine (a calcium channel antagonist) in the current treatment of hypertension. There is a generic brand-name drug Exforge® which has been proven to be clinically effective. However, its price is high, making it quite difficult to access, especially in low- and middle-income countries. Therefore, research and development of generic drugs is essential. In addition, research on simultaneous quantification of amlodipine and valsartan in the dissolution medium must be performed to serve as a basis for comparing in vitro equivalence between the two finished products. Objectives: Investigation of the mobile phase for separating amlodipine and valsartan using the isocratic elution method and validation of the simultaneous quantification of amlodipine and valsartan in three different dissolution media with pH of 1.2, 4.5, and 6.8. Materials and methods: Experimental methods on finished tablets containing amlodipine and valsartan. Results: A procedure for simultaneous quantification of amlodipine and valsartan has been developed and validated in three dissolution media using the HPLC method with DAD detector, ZORBAX Eclipse Plus C18 reversed-phase column (4.6 x 250 mm; 5m), isocratic elution method, detection wavelength of 237 nm, flow rate of 1 mL/min, an injection volume of 20 µL, and mobile phase composed of acetonitrile-triethylamine 0.7% (adjusted to pH 3.0 with 0.05% of phosphoric acid) with a ratio of 40:60. The quantitative method achieves linearity with a correlation coefficient R2>0.999 and the linearity for amlodipine and valsartan was determined in the range at pH of 1.2 (0.25-10 µg/mL and 2-160 µg/mL), at pH of 4.5 and 6.8 (0.5-10 µg/mL and 8-160 µg/mL). The values of amlodipine and valsartan content in the test sample on the same day and between two different days were less than 2.0%. The recovery rate ranged from 98% to 102% with the relative standard deviation (RSD) not exceeding 2.0%. Conclusions: The HPLC method with the above chromatographic conditions can be applied for simultaneous quantification of amlodipine and valsartan in three dissolution media with various pH.