The influence of methyl substitution on the N-demethylation and N-oxidation of normethadone in animal species

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Abstract
N-Monodemethylation and N-oxidation were shown to be the major routes of metabolism of normethadone, (—)-methadone and (—)-isomethadone in vitro by hepatic microsomal preparations from rat, rabbit, guinea-pig, mouse and hamster. The rate of N-oxidation was decreased and the rate of N-demethylation was increased by the introduction of the methyl substituent into normethadone; the configuration of the methyl substituent influenced these processes. Km and Vmax values were determined for liver microsomal N-demethylation of normethadone, (—)-methadone and (—)-isomethadone by rat and guinea-pig and for the N-oxidation of normethadone by guinea-pig. The use of selective inhibitors showed that N-demethylation was not preceeded by N-oxidation in these compounds.