Ethosuximide is an anticonvulsant drug used in the treatment of epilepsy. A simple reverse-phase chromatographic method was developed for the determination of related substances (2-ethyl-2-methylsuccinic acid) in ethosuximide 250 mg soft gelatin capsules. The separation was achieved with the chromatographic conditions including mobile phase composition of acetonitrile:water:glacial acetic acid (25:75:1), C18 column with the dimensions of 150 mm x 3.9 mm, 4 μm, column oven temperature of 25˚C, flow rate of 1.0 ml/min and detector wavelength at 225 nm. The product obeys the Beer’s law. The linear regression formula obtained was y = 16526x + 1098.5 with the correlation coefficients of 0.9982. The method was validated according to ICH guidelines for several parameters such as system suitability, specificity, linearity, limit of detection and quantification, accuracy, precision and robustness. The results conclude that the proposed HPLC method for related substances analysis can be used for routine analysis of ethosuximide soft gelatin capsules.
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