Stability Indicating Simultaneous Validation of Telmisartan and Cilnidipine with Forced Degradation Behavior Study by RP-HPLC in Tablet Dosage Form

A simple, precise, and accurate RP-HPLC method has been developed and validated for the simultaneous assay of Telmisartan and Cilnidipine in tablets. Isocratic RP-HPLC method was developed on Waters C18 ？mm, 5？μm column using mobile phase as acetonitrile (ACN): buffer pH 3.0 with orthophosphoric acid (68？:？32) at a flow rate of 1.0？mL/min and the detection was carried out at 245？nm using photodiode array detector. Forced degradation study was carried out by oxidation, hydrolysis, photolysis, and heating the drug. The method was validated for specificity, linearity, precision, accuracy, robustness, and solution stability. The method was found to be linear in the concentration range of 40–160？μg/mL with correlation coefficient of 0.9990 for Telmisartan and 10–40？μg/mL with correlation coefficient of 0.9989 for Cilnidipine. Degradation products produced as a result of stress studies did not interfere with the detection of agomelatine; therefore, the assay can be considered to be stability indicating. 1. Introduction Telmisartan is chemically nominated as 4′-[(1,4′-dimethyl-2′-propyl[2,6′-bi-1H-benzimidazole]-1′-yl) methyl] [1,1′-biphenyl]-2-carboxylic acid (Figure 1). Its molecular formula is C33H30N4O2 and molecular weight is 514.62. It is a diabetes angiotensin receptor blocker that shows high affinity for the angiotensin II type 1 (AT1) receptors, has a long duration of action, and has the longest half-life of any angiotensin II receptor blocker (ARB) [1]. In clinical studies, Telmisartan shows comparable antihypertensive activity to other major antihypertensive classes, such as angiotensin converting enzyme (ACE) inhibitors, beta-blockers, and calcium antagonists [2]. Figure 1: Chemical structure of Telmisartan. Cilnidipine is chemically nominated as 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridine carboxylic acid 2-methoxyethyl(2E)-3-phenyl-propenyl ester (Figure 2). It is a dual blocker of L-type voltage-gated calcium channels in vascular smooth muscle and N-type calcium channels in sympathetic nerve terminals that supply blood vessels [3]. Figure 2: Chemical structure of Cilnidipine. The parent drug stability test guideline Q1A (R2) issued by the International Conference on Harmonization (ICH) suggests that stress testing is an essential part of development strategy and is carried out under more serve condition than accelerated conditions. These studies provide information to establish its inherent stability characteristics, leading to identification of degradation products and hence supporting the suitability of the proposed analytical