Stability Kinetics of Imiquimod: Development and Validation of an Analytical Method

For a new immune modulator imiquimod, various liquid chromatography methods have been described in literature but all of them are deficient in one or other aspects of complete method development. The present work intends to develop and validate the stability indicating reverse phase high performance liquid chromatographic (HPLC) method. The isocratic flow of mobile phase comprising equal volume ratio of acetate buffer BP pH 3.7 and acetonitrile at the rate of 1.5 mL/min through the C-18 column at 25°C lead to elution of drug around 2.3 min when analyzed at 244 nm using UV-detector. The linear regression equation in calibration plot was y = 61632×-1224 with 0.9992 coefficient of determination (r2). The percent relative standard variation (% RSD) in peak area at low, mid and high region of linearity range was less than 5% in precision studies. The method was able to detect 0.039 μg/mL of drug but practical limit of quantitation (LOQ) was 1.5 μg/mL. The imiquimod molecule was stable in all except oxidizing conditions where it degraded into more polar molecule in hydrogen peroxide (H2O2) concentration dependent manner. Therefore, an analytical method capable of accurately and specifically estimating the drug in microgram range was successfully developed.