Simultaneous Estimation of Apremilast and Betamethasone Dipropionate in Microsponge-Based Topical Formulation using a Stability Indicating RP-HPLC Method: A Quality-by-Design Approach

A stability-indicating reverse phase high-performance liquid chromatography method was developed and validated for simultaneous quantification of apremilast (APL) and betamethasone dipropionate (BD) in bulk as well as drug loaded microsponges. Various mobile phase systems were screened to check the system suitability followed by force degradation analysis to determine APL and BD stability under varying stress conditions. A central composite design model was used to optimize the column temperature and flow rate using Design Expert® (9.0.1). One factor at a time approach with five independent factors were used to validate the robustness of the method. Finally, APL and BD were precisely and accurately quantified from drug loaded microsponges using the validated method. A favorable separation of APL and BD was obtained on a Phenomenex® Luna C18 column using a mixture of 50 mM phosphate buffer containing 0.1% triethylamine (pH 6.1) and acetonitrile (60:40%v/v) as mobile phase. Both the drugs were found to be stable when exposed to stressors such as heat-, light-, alkali-, acid- and peroxide-induced degradation. The calibration curves were found to be linear with appreciable limit of detection and limit of quantification. Recovery and percentage relative standard deviation of peak areas for APL and BD were found to be < 2.0% and 99-100% in bulk drug solution and <2.0% and 99-103% in microsponge formulation, respectively. Statistical analysis using analysis of variance indicated that the model was significant (P < 0.001). Hence, the developed method can be effectively used to quantify APL and BD, both in bulk as well as microsponge formulations.