Method Development and Validation of Promethazine HCl by Using RP-HPLC and Its Forced Degradation Studies

A simple, rapid, sensitive, and stability-indicating reverse-phase high-performance liquid chromatography (RP-HPLC) method was developed and validated for the quantitative determination of promethazine hydrochloride (HCl) in pharmaceutical formulations. Chromatographic separation was achieved using a SunFire® C18 column (4.6 × 250 mm, 5 µm) with a mobile phase consisting of acetonitrile and 0.1% orthophosphoric acid in water (80:20, v/v) at a flow rate of 1.0 mL/min. Detection was performed at 249 nm using a photodiode array detector. The developed method was validated according to the International Council for Harmonisation Q2 guidelines with respect to specificity, linearity, precision, accuracy, robustness, limit of detection, and limit of quantitation.The method exhibited good linearity over the concentration range of 2–64 µg/mL with a correlation coefficient ( R 2 ) of 0.9993. The percentage relative standard deviation for precision studies was below 2%, indicating satisfactory repeatability and reproducibility. Forced degradation studies were performed under acidic, alkaline, neutral, oxidative, and thermal stress conditions to evaluate the stability indicating capability of the method. Additional chromatographic peaks corresponding to degradation products were observed in acid, base, neutral, and oxidative stress conditions, while minimal degradation was observed under thermal stress. Furthermore, liquid chromatography–mass spectrometry (LC-MS) analysis was carried out to characterize the degradation products formed during stress studies. LC-MS results indicated that alkaline stress produced the highest degree of degradation, whereas thermal stress generated only minor residual impurities, confirming the relative stability of promethazine HCl under thermal conditions. The developed RP-HPLC method was found to be suitable for routine quality control analysis and stability assessment of promethazine HCl in pharmaceutical formulations.