DEVELOPMENT AND VALIDATION OF RP-HPLC METHOD FOR SIMULTANEOUS ESTIMATION OF AZILSARTAN MEDOXIMIL AND CHLORTHALIDONE IN BULK FORM AND FORMULATION USING QUALITY BY DESIGN Original Article SANDEEP KUMAR SOHNI 1 , ROBIN KUMAR 2 , MYMOONA AKHTAR 1 , CHANDA RANJAN 1 , GITA CHAWLA 1* 1 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New Delhi 110062, India, 2 Received: 13 Aug 2015 Revised and Accepted: 30 Dec 2015 Reference Standard Division, Indian Pharmacopoeia Commission, Ministry of Health and Family Welfare, Govt. of India, Sector-23, Rajnagar, Ghaziabad 201002, India Email: gchawla@jamiahamdard.ac.in ABSTRACT Objective: Development of an accurate, precise, robust, sensitive, economical and rapid isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) method complying quality by design (QbD) trends for simultaneous estimation of azilsartan medoximil and chlorthalidone in bulk and formulation form and validation of the method as per ICH guidelines. Methods: The simultaneous estimation of the drugs-azilsartan and chlorthalidone was performed using C8 column having dimensions 150×4.6 mm×5 µm, injection volume 10 µl, flow rate 0.8 ml/min., runtime 10 min., column temperature 20 o Results: The retention times for chlorthalidone and azilsartan medoxomil were 2.4 min. and 5.1 min. respectively with resolution 17. The method was validated as per the ICH guidelines. The linearity of chlortalidone and azilsartan medoxomil was in the range of 6.3 to 15 µg/ml and 20 to 48 µg/ml respectively. The potency of the formulation was found to be 108.12 % and 98.20 % respectively, which are within acceptable limits as per IP. C, sampler temperature 5 °C and ultraviolet detection using a photodiode array detector at 220 nm as constant. The optimized method was validated as per ICH guidelines. Conclusion: Method validation results have proven the method to be selective, precise, accurate, and robust, as well as stability indicating. The C8 column used for analysis gave encouraging results with better resolution and less retention time. This method can be successfully applied for the routine analysis involving the determination of content uniformity and dissolution profiling as well as stability study by the industry. Keywords: RP-HPLC, QbD, ICH, Azilsartan medoximil, Chlorthalidone. © 2016 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/ ) INTRODUCTION Azilsartan medoximil, chemically, (5-methyl-2-oxo-1,3-dioxol-4- yl)methyl 2-ethoxy-1-{[2’-(5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl) biphenyl-4-yl]methyl}-1H-benzimidazole-7 carboxylate mono- potassium salt (fig. 1), is a new addition to the angiotensin receptor blocker (ARB) class of antihypertensive agents [1]. As an ARB, azilsartan medoxomil selectively inhibits angiotensin II from binding to the angiotensin II type-1 receptors (AT1) which causes the blocking of the pressor effects of angiotensin II and leads to antihypertensive activity [2, 3]. Azilsartan medoxomil is a type of prodrug. It gets hydrolysed to the active moiety, azilsartan, in the gastrointestinal (GI) tract during the absorption phase. The enzyme, principally responsible for the metabolism of azilsartan is cytochrome P450 (CYP) 2C9. Azilsartan is metabolized to two primary metabolites, M-I, and M-II, by decarboxylation and O- dealkylation, respectively. These metabolites have low affinity for the AT1 receptors and therefore, have no effect on the pharmacological activity of azilsartan medoxomil. Azilsartan medoximil is a white crystalline powder that is insoluble in water, freely soluble in methanol, soluble in acetic acid, slightly soluble in acetone and acetonitrile [4-6]. Chlorthalidone, chemically 2-chloro- 5(1-hydroxy-3-oxo-1isoindolinyl) benzene sulphonamide (fig. 2), is a thiazide-like diuretic/antihypertensive. Chlorthalidone is a white or yellowish-white crystalline powder, practically insoluble in water, ether and chloroform, soluble in methanol and slightly soluble in ethanol. Chlorthalidone produces diuresis with increased excretion of sodium and chloride. The cortical diluting segment of the ascending limb of Henle's loop of the nephron is the site of action. The diuretic effects of chlorthalidone lead to the reduction in extracellular fluid volume, plasma volume, cardiac output, total exchangeable sodium, glomerular filtration rate, and renal plasma flow [3]. Variations in diuretic-mediated inhibition of carbonic anhydrase-dependent chloride transport in platelets and vascular smooth muscle could account for the contrasting efficacy of the thiazide and thiazide-like diuretics in reducing cardiovascular morbidity in patients with hypertension [7]. Fig. 1: Chemical structure of Azilsartan Fig. 2: Chemical structure of Chlorthalidone The combination of azilsartan medoximil and chlorthalidone has International Journal of Pharmacy and Pharmaceutical Sciences ISSN- 0975-1491 Vol 8, Issue 2, 2016