Determination of metoclopramide and two of its metabolites using a sensitive and selective gas chromatographic-mass spectrometric assay.

A modified gas chromatographic-mass spectrometric (GC-MS) assay has been developed to quantitate metoclopramide (MCP) and two of its metabolites [monodeethylated-MCP (mdMCP), dideethylated-MCP (ddMCP)] in the plasma, bile and urine of sheep. The heptafluorobutyryl derivatives of the compounds were formed and quantitated using electron-impact ionization 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 obtained from non-pregnant sheep. Sample preparation has been simplified and the method is more selective and sensitive (2 fold) than our previous assay using electron-capture detection. The limit of quantitation for MCP, mdMCP and ddMCP was 1 ng/ml in plasma, urine and bile, requiring 0.5 ml of sample. This represents 2.5 pg of the analytes at the detector. 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, recoveries ranged from 56.5-87.8%, 61.5-87.5%, 62.6-90.2% for MCP, mdMCP and ddMCP, respectively. Recoveries in bile ranged from 83.5-100.9%, 78.5-90.5%, 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 in 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 concentration 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 plasma and urine of a non-pregnant ewe is demonstrated.