Analytical 'Quality-by-Design' paradigm in development of a RP-HPLC method for the estimation of cilnidipine in nanoformulations: Forced degradation studies and mathematical modelling of in-vitro release studies

The present study focuses on optimizing, developing, and validating a sensitive and specific reversed-phase high-performance liquid chromatography (RP-HPLC) method for the quantification of cilnidipine (CLD) in bulk and nanoformulations. Design of Experiments was employed to optimize the RP-HPLC method. The critical method parameters (CMPs) were screened using the Taguchi OA design. The selected parameters were further optimized using the Box-Behnken design with the retention time (Rt), peak area, number of theoretical plates (NTP) and tailing factor (Tf) as the dependent variables. The optimized chromatographic parameters for the RP-HPLC method were: concentration of acetonitrile: 78% v/v, flow rate: 0.7 mL/min and oven temperature: 25 C. The Rt, peak area, NTP and Tf were 9.03 min, 1174428 mV-min, 11054 and 1.133 respectively. The optimized method demonstrated excellent linearity (R2 = 0.9998) having a range of 50-4000 ng/mL and LOD and LOQ were 6.76 and 20.48 ng/mL, respectively. The sensitivity, accuracy, precision, specificity and robustness of the developed RP-HPLC method was in accordance with the regulatory guidelines. It also exhibited specificity for CLD in the presence of degradation products. The RP-HPLC method was successfully employed to estimate the drug content of CLD nanocrystals as well as for in-vitro dissolution study.