Capillary Electrophoresis Method for Quantification of Naltrexone and Its Major Metabolite 6‐β‐Naltrexol in Human Plasma

In this study, a capillary electrophoresis (CE) method was developed for the determination of naltrexone, an opioid antagonist, and its primary metabolite, 6-β-naltrexol (6-β-NTX). Naltrexone is commonly used in the treatment of opioid and alcohol dependence. Accurate quantification of such drugs and their metabolites is essential for ensuring therapeutic efficacy and safety. Reliable determination of NTX and 6-β-NTX in plasma is important for bioanalytical and clinical investigations involving naltrexone therapy. Method optimization was carried out using Box-Behnken design within the framework of response surface methodology to achieve maximum resolution between naltrexone and 6-β-naltrexol. Separation was performed at 15°C using a 10 mM phosphate buffer (pH 2.0) under an applied voltage of 20 kV, without the addition of organic modifiers. The method was validated in accordance with bioanalytical validation guidelines, providing a validated lower limit of quantification (LLOQ) of 0.05 µg/mL for both analytes, with precision (% relative standard deviation [RSD]) below 7% at the LLOQ. The validated method was successfully applied to plasma samples obtained from patients receiving treatment for alcohol and opioid use disorders. Furthermore, the environmental sustainability of the proposed CE method and its sample preparation steps was assessed using green analytical chemistry metrics, such as AGREE, AGREEprep, and MoGAPI, demonstrating its greener profile compared to reported methods.