Isolation and characterization of a degradation product of mexiletine hydrochloride using FT-IR, LC-MS and NMR: method development and validation of stability indicating RP-HPLC method for quantification of characterized impurity

Abstract

Mexiletine Hydrochloride is an antiarrhythmic drug used to treat acute and chronic ventricular arrhythmias. Significant degradation of unknown impurity was observed while evaluating the impurity profile of the Mexiletine Hydrochloride stability studies. The levels of the unknown impurity are more than the regulatory identification/qualification threshold level (0.08%). Mexiletine was forcefully subjected to various stress conditions, such as acidic, basic, oxidation, photolysis, and thermal. Among these stress conditions, we identified an unknown degradation impurity in the thermal stress (105°C for 15 days) of Mexiletine, the same as that of an unknown impurity observed in the stability studies. The present research reports the isolation of unknown impurity in thermal stress by preparative HPLC and the characterization of isolated unknown degradation impurity using LC-MS, FT-IR, and NMR techniques. The spectral data elucidated the structure of the degradation product, and it was identified as “(E)-2-(((1-(2,6-dimethylphenoxy)propan-2-yl)imino)methyl)-6-methylphenol”. A stability-indicating HPLC method was developed and validated to determine and quantify the degradation product in Mexiletine Hydrochloride. The levels of the unknown degradation product reduced to below the limit of detection (<0.007%) from 0.10% after applying its relative response factor “16.5” and complying with the regulatory threshold limits. It helps to extend the shelf life of Mexiletine.