Development and validation of colorimetric method for the determination of pregabalin in bulk and pharmaceutical formulations

A simple, accurate and precise colorimetric method was developed for the quantification of pregabalin (PGN) in bulk and pharmaceutical formulations. The method was based on the production of a colored complex by reacting PGN with ascorbic acid in DMSO solvent. The resultant complex exhibits absorption maxima at 390 and 532 nm. The factors that affect the complex development and stability were studied and optimized. The reaction stoichiometry of drug: reagent was found to be 1:2. The method was then validated according to ICH guidelines. Regression analysis of Beer's plot showed good correlation (r2 value more than 0.998) within a concentration range of 5-30μg/ml. Linearity was confirmed by standardized residuals versus fitted value plots using Minitab14 software. The limits of detection and quantification at 390 and 532nm were 1.34μg/ml, 1.09μg/ml and 4.05μg/ml, 3.294μg/ml, respectively. Added recovery measurements were found to be 100.04±2.07% and 99.58 ±1.98% at 390nm and 532nm, respectively, which reflect the accuracy of the method and freedom from interference (relative standard deviation values were less than or equal 0.2%). The average assay for the commercial capsule preparation (PGN 150mg/capsule) was found to be 101.373±0.49 and 101.812±0.73 at 390 and 532nm, respectively. The developed method is an inexpensive, extraction free and can be applied for routine analysis of PGN in most of analytical laboratories.