Mass Spectrometric Characterization of Plasma Mebeverine Metabolites and Its Synthesis

Abstract

Mebeverine is a musculotropic antispasmodic drug that is widely used in the treatment of irritable bowel syndrome. As an ester of mebeverine alcohol and veratric acid, mebeverin is quickly metabolized and is practically undetectable in blood plasma. The main goal of this work was establishing the structure of the main metabolites of mebeverin in human blood plasma. The study was conducted by time-of-flight mass spectrometry (LC-IT-TOF MS), metabolites of mebeverine were extracted from plasma with acetonitrile. When comparing chromatograms of blood plasma obtained before and after drug administration, four main peaks of metabolites were detected. To establish the structure of the compounds, mass spectra of the first and second order were taken. The first-order spectra were used to calculate the metabolite formula and the structure was determined from the fragmentation spectra, as well as by comparing the fragmentation spectra of mebeverine and its proposed metabolites. The proposed compounds were synthesized, and their structure was confirmed using NMR and chromatography-mass spectrometry. Four main metabolites were found in this study: desmethylmebeverine acid (DMAC), glucuronide product of DMAC (DMAC-Glu), mebeverine acid (MAC) and mebeverine alcohol (MAL). The results complement the available literature data about the veratric acid metabolism, urine, and microsomal studies. According to the data obtained, the main metabolite of mebeverine in the blood is DMAC. The concentration of MAC after mebeverine administration is almost ten times less than DMAC, the content of MAL and DMAC-Glu is insignificant, and probably does not affect the pharmacological effect of mebeverine. Therefore, the concentration of DMAC is the main parameter to be monitored in pharmacokinetics studies.