Stability‐Indicating RP‐HPLC Method for Lopinavir Estimation in Pharmaceutical Co‐Crystals: A Design of Expert Approach

ABSTRACT The primary objective of this investigation was to develop and validate a robust reversed‐phase high‐performance liquid chromatography (RP‐HPLC) method for the quantification of lopinavir in co‐crystals formed with fumaric acid and acetamide. A Box–Behnken design within the design of the experiment framework was employed to optimize chromatographic conditions. The method utilized a Phenomenex Luna C18 column and a mobile phase of methanol and 0.1% formic acid (80:20 v/v) at a flow rate of 1 mL/min, with detection at 259 nm. Validation followed ICH Q2 (R1 and R2) guidelines, confirming the method's specificity, accuracy, precision, linearity, and robustness. Co‐crystals of lopinavir were prepared using liquid‐assisted grinding and reaction crystallization techniques. The validated HPLC method successfully quantified lopinavir in these co‐crystals, with recovery rates ranging from 96.3% to 99.8%. Forced degradation studies under various stress conditions (acidic, base, oxidative, thermal, and photolytic) demonstrated the method's capability to distinguish lopinavir from its degradation products. In conclusion, the developed RP‐HPLC method is suitable for routine analysis and quality control of lopinavir in co‐crystal formulations. This method not only provides precise quantification but also offers insights into the enhanced delivery potential of lopinavir through co‐crystallization, contributing to improved therapeutic efficacy in HIV/AIDS treatment.