Determination of Related Substances in Promethazine Hydrochloride and Dextromethorphan Hydrobromide in Oral Solution by RP-HPLC Method.

The goal of this study is to provide a single, widely applicable high-performance liquid chromatographic (HPLC) technique for the determination of related substances in multicomponent oral solution of promethazine hydrochloride and dextromethorphan hydrobromide. For the assessment of impurities of promethazine hydrochloride and dextromethorphan hydrobromide in oral solution, a unique, sensitive, quick, stability-indicating gradient HPLC technique has been created. For chromatographic separation, an Agilent Eclipse XDB-C18, 250 mm × 4.6 mm, 5 μm column was used with a buffered mobile phase consisting of a mixture of potassium dihydrogen phosphate pH 3.0:acetonitrile (80:20) v/v as mobile phase A and potassium dihydrogen phosphate pH 3.0:acetonitrile:methanol (10:10:80) v/v/v as mobile phase B. The separation was performed at a flow rate of 1.2 mL/min and a detection wavelength of 224 nm. The temperature of the column oven was regulated at 40°C. With good sensitivity and resolution, all compounds were effectively separated on a reverse-phase HPLC column. Acid, base, photolytic, thermal, oxidative and humidity stress conditions significantly degraded dextromethorphan hydrobromide and promethazine hydrochloride. The developed technique was validated according to the criteria of the International Conference on Harmonization for all validation parameters such as specificity, accuracy, linearity, precision, the limit of detection, the limit of quantitation and robustness.