DETERMINATION OF METOCLOPRAMIDE AND 2 OF ITS METABOLITES USING A SENSITIVE AND SELECTIVE GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC ASSAY

A modified gas chromatographic-mass spectrometric (GC-MS) assay has be en developed to quantitate metoclopramide (MCP) and two of its metabol ites [monodeethylated-MCP (mdMCP), dideethylated-MCP (ddMCP)] in the p lasma, bile and urine of sheep. The heptafluorobutyryl derivatives of the compounds were formed and quantitated using electron-impact ioniza tion in the selected-ion monitoring mode (MCP, m/z 86, 380; mdMCP, m/z 380 and ddMCP, m/z 380). No interference was observed from endogenous compounds following the extraction of various biological fluids obtai ned from non-pregnant sheep. Sample preparation has been simplified an d the method is more selective and sensitive (2 fold) than our previou s assay using electron-capture detection. The limit of quantitation fo r MCP, mdMCP and ddMCP was 1 ng/ml in plasma, urine and bile, requirin g 0.5 ml of sample. This represents 2.5 pg of the analytes at the dete ctor. The standard curves were linear over a working range of 1-40 ng/ ml. Absolute recoveries in plasma ranged from 76.5-94.7%, 79.2-96.8%, 80.3-102.2% for MCP, mdMCP and ddMCP, respectively. In urine, recoveri es ranged from 56.5-87.8%, 61.5-87.5%, 62.6-90.2% for MCP, mdMCP and d dMCP, respectively, Recoveries in bile ranged from 83.5-100.9%, 78.5-9 0.5%, 66.9-79.2% for MCP, mdMCP and ddMCP, respectively. Overall intra -day precision ranged from 2.9% for MCP in plasma to 12.6% for mdMCP i n bile. Overall inter-day precision ranged from 5.9% for MCP in urine to 14.9% for ddMCP in bile. Bias was the greatest at the 1 ng/ml conce ntration in all biological fluids ranging from a low of 2.4% for mdMCP in plasma to a high of 11.9% for ddMCP in urine. Applicability of the assay for pharmacokinetic studies of MCP, mdMCP and ddMCP in the plas ma and urine of a non-pregnant ewe is demonstrated.