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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: OBJECTIVE, METHODS, RESULTS. Meshes: Aryl Hydrocarbon Hydroxylases, Catalysis, Cytochrome P-450 CYP2C19, Doxepin, Humans, Isoenzymes, Isothiocyanates, Microsomes, Liver, Mixed Function Oxygenases, Tranylcypromine.
user
Is the N-demethylation of the doxepin isomers mainly catalyzed by the polymorphic CYP2C19? Context: This study was conducted to identify the cytochrome P450s (CYPs) responsible for the metabolism of the cis- and trans-isomers of the tricyclic antidepressant doxepin to its pharmacologically active N-desmethylmetabolite by in vitro techniques. The doxepin N-demethylation was studied by means of pooled human liver microsomes and chemical inhibitors, recombinant human (rh)-CYPs, and geno- and phenotyped human liver microsomes. The N-demethylation of both isomers was inhibited most prominently by tranylcypromine (CYP2C19) to more than 50%. Furafylline (CYP1A2) and sulfaphenazole (CYP2C9) inhibited the N-demethylation to a lesser extent while quinidine (CYP2D6) or troleandomycine (CYP3A4) had no effect. Rh-CYP2C19, -CYP1A2, and -CYP2C9 were able to N-demethylate cis- and trans-doxepin. Only traces of trans-desmethyldoxepin were detectable when CYP3A4 was used. The maximum velocity in the cis- and transdoxepin N-demethylation was significantly (P < 0.05) lower in microsomes with low CYP2C19 activity (345 +/- 44 and 508 +/- 75 pmol/min/ mg protein, respectively) compared to those with high CYP2C19 activity (779 +/- 132 and 1,189 +/- 134 pmollmin/mg).
assistant
The present study demonstrates a significant contribution of the polymorphic CYP2C19 to the N-demethylation of doxepin. CYP2C9 and CYP1A2 play a minor role and CYP3A4 does not contribute substantially. Final Decision: yes