AQbD-guided development of a robust and green SI-RP-HPLC method for impurity profiling of an efonidipine hydrochloride ethanolate and chlorthalidone combination, with LC-MS and NMR-based identification of degradation product in efonidipine.

Abstract

Efonidipine Hydrochloride Ethanolate (EHE) and Chlorthalidone (CTD) are co-formulated for the management of hypertension owing to their complementary pharmacological actions. Ensuring accurate impurity profiling in such combination formulations is vital for maintaining drug stability, safety and regulatory compliance. However, conventional analytical techniques often face challenges related to sustainability and robustness. Reverse Phase High-Performance Liquid Chromatography (RP-HPLC) remains a key analytical approach for impurity determination, yet the integration of Quality by Design (QbD) principles into its development is still evolving. The present study focuses on developing a novel, sustainable RP-HPLC method for impurity profiling of EHE and CTD tablets using a QbD approach and green chemistry. Chromatographic separation was achieved on a Zorbax SB C8 column (150 mm × 4.6 mm, 5 µm). Critical method parameters such as mobile phase composition and pH were systematically optimized through QbD to enhance method robustness. A photolytic degradation product of EHE was identified as Efonidipine Related Compound A, and a plausible photolytic degradation pathway was proposed. A photolytic degradation product was identified in the LC-MS and its structure was confirmed through NMR spectroscopy. The developed green method exhibited excellent resolution, precision and reproducibility across multiple batches, allowing for effective separation and quantification of impurities. This green QbD-optimized, environmentally sustainable RP-HPLC method provides a reliable and scalable solution for impurity profiling in complex pharmaceutical formulations, aligning with modern quality control and regulatory expectations.