PT - JOURNAL ARTICLE AU - Kelsey L. Hanson AU - Brooke M. VandenBrink AU - Kantipudi N. Babu AU - Kyle E. Allen AU - Wendel L. Nelson AU - Kent L. Kunze TI - Sequential Metabolism of Secondary Alkyl Amines to Metabolic-Intermediate Complexes: Opposing Roles for the Secondary Hydroxylamine and Primary Amine Metabolites of Desipramine, (<em>S</em>)-Fluoxetine, and <em>N-</em>Desmethyldiltiazem AID - 10.1124/dmd.110.032391 DP - 2010 Jun 01 TA - Drug Metabolism and Disposition PG - 963--972 VI - 38 IP - 6 4099 - http://dmd.aspetjournals.org/content/38/6/963.short 4100 - http://dmd.aspetjournals.org/content/38/6/963.full SO - Drug Metab Dispos2010 Jun 01; 38 AB - Three secondary amines desipramine (DES), (S)-fluoxetine [(S)-FLX], and N-desmethyldiltiazem (MA) undergo N-hydroxylation to the corresponding secondary hydroxylamines [N-hydroxydesipramine, (S)-N-hydroxyfluoxetine, and N-hydroxy-N-desmethyldiltiazem] by cytochromes P450 2C11, 2C19, and 3A4, respectively. The expected primary amine products, N-desmethyldesipramine, (S)-norfluoxetine, and N,N-didesmethyldiltiazem, are also observed. The formation of metabolic-intermediate (MI) complexes from these substrates and metabolites was examined. In each example, the initial rates of MI complex accumulation followed the order secondary hydroxylamine &gt; secondary amine ≫ primary amine, suggesting that the primary amine metabolites do not contribute to formation of MI complexes from these secondary amines. Furthermore, the primary amine metabolites, which accumulate in incubations of the secondary amines, inhibit MI complex formation. Mass balance studies provided estimates of the product ratios of N-dealkylation to N-hydroxylation. The ratios were 2.9 (DES-CYP2C11), 3.6 [(S)-FLX-CYP2C19], and 0.8 (MA-CYP3A4), indicating that secondary hydroxylamines are significant metabolites of the P450-mediated metabolism of secondary alkyl amines. Parallel studies with N-methyl-d3-desipramine and CYP2C11 demonstrated significant isotopically sensitive switching from N-demethylation to N-hydroxylation. These findings demonstrate that the major pathway to MI complex formation from these secondary amines arises from N-hydroxylation rather than N-dealkylation and that the primary amines are significant competitive inhibitors of MI complex formation. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics