Quantification of Dimethylacetamide and its Primary Metabolite Monomethylacetamide in Plasma Using Robust LC-MS Method

Abstract

N,N-Dimethylacetamide (DMA) is an excellent solvent that is highly used in the production of synthetic fibres as well as in the pharmaceutical industry. It is present as a solvent in the intravenous formulation of busulphan, a drug used in high doses as myeloablative treatment prior to hematopoietic stem cell transplantation (SCT). DMA was shown to cause hepatotoxicity as well as neurotoxicity, as revealed throughout several studies including phase I study. In the present investigation we developed an LC-MS based method to detect and quantify DMA and its primary metabolite N-monomethylacetamide (MMA) simultaneously in human plasma, using a C-18 ODS-AQ/S-5 µm 12 nm separation column. The lower limits of quantification (LLOQs) for DMA and MMA were 1.8 µM and 8.6 µM, respectively. The limit of detection (LOD) for DMA and MMA were 0.53 µM and 2.52 µM, respectively. The recovery of DMA from plasma ranged from 97-101% and for MMA from 76-100%. The stability for DMA and MMA was assessed through freeze-thaw cycles and storage at different temperatures (RT, 4°C and -20°C for three days); the results have shown <7.9% CV for DMA and <14.1% for MMA. The inter-day and intra-day variation assay accuracy and precision was <6.3% for DMA and <8.6% for MMA. The calibration was linear within the ranges 1 to 4000 µM. The method was applied to follow the kinetics and to quantify DMA and its metabolite MMA in 49 plasma samples from 2 patients undergoing SCT and treated with intravenous busulphan that contain DMA. The present method is simple, robust and showed good selectivity with high accuracy, precision and reproducibility. Moreover, it can be utilized to determine DMA and its metabolite in workers, patients and environment and hence avoid toxic exposure.