Development and Validation of a Stability-Indicating RP-HPLC Method for Simultaneous Quantification of Cilnidipine and Telmisartan in Pharmaceutical Formulations

A rapid, sensitive, and precise reverse-phase high-performance liquid chromatographic (RP-HPLC) method was developed and validated for simultaneous quantification of Cilnidipine and Telmisartan in pharmaceutical formulations. The chromatographic separation was achieved using an Agilent C18 column (2.5 μm; 4.6×100 mm) with an isocratic mobile phase consisting of methanol:0.1% triethylamine (pH 6.0 adjusted with orthophosphoric acid) in the ratio of 60:40 v/v at a flow rate of 0.9 mL/min. Detection was carried out at 251 nm wavelength. The retention times for Cilnidipine and Telmisartan were 2.382 and 3.315 minutes, respectively. The method demonstrated linearity over concentration ranges of 2-10 μg/mL for Cilnidipine and 1.5-7.5 μg/mL for Telmisartan with correlation coefficients (R²) of 0.999. The limits of detection were 0.0843 and 0.0084 μg/mL, while the limits of quantification were 0.255 and 0.025 μg/mL for Cilnidipine and Telmisartan, respectively. The method was validated according to ICH guidelines for accuracy, precision, specificity, linearity, robustness, and ruggedness. Forced degradation studies revealed that both drugs underwent significant degradation under oxidative conditions (6.02% for Cilnidipine and 21.15% for Telmisartan), while showing minimal degradation under neutral conditions. The developed method found to be suitable for routine quality control analysis of Cilnidipine and Telmisartan in pharmaceutical formulations.