Development and Validation of Stability Indicating RP-HPLC Method for Simultaneous Determination of Chlorthalidone and Amlodipine Besylate in Bulk and in Tablet Dosage Form

Rapid, simple, and novel isocratic reverse-phase high-performance liquid chromatography (RP-HPLC) method was developed with stability, indicating potential for simultaneous estimation of chlorthalidone and amlodipine besylate in bulk and in tablet dosage form. The chromatographic elution was performed on Merck's Oyster ODS3 (5 mu m, 150 mm x 4.6 mm i.d.) column with 20 mM phosphate buffer pH 2.5: methanol: acetonitrile (40:30:30, v/v/v) at flow rate 1.0 mL/min pumped through a column maintained at ambient temperature (about 25 degrees C) with a response observed at 238 nm over an 8 min run time. The chlorthalidone and amlodipine were eluted at 2.219 min and 4.120 min, respectively. The method was linear: 74.9767 - 174.9455 mu g/mL (R2 = 0.999) for chlorthalidone and 30.2266 - 70.5288 mu g/mL (R2 = 0.999) for amlodipine. The percentage recovery average at three different levels was found to be 99.53, 99.47 and 98.32% for chlorthalidone and 101.23, 98.75 and 99.10% for amlodipine. The % RSD value was below 2.0 during the precision study. The mobile phase was stable for 2 days; preparations of standard and sample were stable at room temperature and refrigerated (2 - 8 degrees C) for day 1. Additionally, the method is stability indicating, as it was able to distinguish the degraded product generated during forced degradation from active analytes. The method was validated according to the International Conference on Harmonization (ICH) guideline Q2 (R1) and can be used successfully for stability study and routine analysis.