The metabolic pathways involved in the metabolism are not well-characterized. In any case, the cytochrome P450 enzymes CYP3A4, CYP2D6, and CYP1A2 may all be involved to varying extents. Trazodone is known to be extensively metabolized by the liver via hydroxylation, "N"-oxidation, and "N"-dealkylation. Several metabolites of trazodone have been identified, including a dihydrodiol metabolite (via hydroxylation), a metabolite hydroxylated at the "para" position of the "meta"-chlorophenyl ring (via CYP2D6), oxotriazolepyridinepropionic acid (TPA) and mCPP (both via "N"-dealkylation of the piperazinyl nitrogen mediated by CYP3A4), and a metabolite formed by N-oxidation of the piperazinyl nitrogen. CYP1A2, CYP2D6, and CYP3A4 genotypes all do not seem to predict concentrations of trazodone or mCPP. In any case, there are large interindividual variations in the metabolism of trazodone. In addition, poor metabolizers of dextromethorphan, a CYP2D6 substrate, eliminate mCPP more slowly and have higher concentrations of mCPP than do extensive metabolizers.