Selected ion monitoring analysis of conjugated metabolites of methadone using biosynthetic internal standards for the study of methadone-diazepam interaction

A methadone-diazepam interaction study in rats was performed in which conjugated metabolites of methadone were analyzed using deuterated biosynthetic internal standards. Diazepam (5mg/kg) was given to rats through a cannulate djugular vein and a subcutaneous dose of methadone (10mg/kg) was given. Bile was collecte through the cannulate dbile duct over a period of 24 hours. The deuterium label of the internal standards was found to be stable under conditions of the prolonged incubation. There was no significant difference in the excretion of the metabolites between the control and the diazepam treated rats. Feasibility of using biosynthetic internal standards with selected ion monitoring was established for the drug metabolism and kinetic studies.