Identification of the human cytochrome P450 isoforms mediating in vitro N-dealkylation of perphenazine

Br J Clin Pharmacol. 2000 Dec;50(6):563-71. doi: 10.1046/j.1365-2125.2000.00298.x.


Aims: To identify the human cytochrome P450 (CYP) isoforms mediating the N-dealkylation of the antipsychotic drug perphenazine in vitro and estimate the relative contributions of the CYP isoforms involved.

Methods: cDNA-expressed CYP isoforms were used to identify the isoforms that are able to mediate the N-dealkylation of perphenazine, which is considered a major metabolic pathway for the drug. Using human liver microsomal preparations (HLM), inhibition studies were carried out to establish the relative contributions of the CYP isoforms involved in the N-dealkylation reaction.

Results: CYP isoforms 1A2, 3A4, 2C8, 2C9, 2C18, 2C19 and 2D6 were able to mediate the N-dealkylation of perphenazine. Reaction velocities and their relative abundance in HLM suggested that CYP1A2, 3A4, 2C19 and 2D6 were the most important contributors to N-dealkylation. Apparent Km values of CYP1A2 and CYP2D6 were in the range 1-2 microM, and Km values of CYP2C19 and CYP3A4 were 14 microM and 7.9 microM, respectively. Ketoconazole inhibition of N-dealkylation mediated by a mixed HLM indicated that CYP3A4 accounted for about 40% of perphenazine N-dealkylation at therapeutically relevant concentrations. The contribution of the CYP isoforms 1A2, 2C19 and 2D6 amounted to 20-25% each as measured by the percentage inhibition obtained by addition of furafylline, fluvoxamine or quinidine, respectively. HLM-mediated N-dealkylation of perphenazine accounted for 57% of the total amount of substrate consumed during incubation.

Conclusions: The present in vitro study suggests that CYP isoforms 1A2, 3A4, 2C19 and 2CD6 are primarily involved in the N-dealkylation of perphenazine. The relatively modest role of CYP2D6 is at variance with in vivo studies, which indicate a greater contribution of this isoform. Alternative metabolic pathways, corresponding to 43% of the HLM-mediated metabolism of the drug, may depend more strongly on CYP2D6.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkylation
  • Antipsychotic Agents / metabolism*
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / classification
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • Enzyme Inhibitors / pharmacology
  • Humans
  • In Vitro Techniques
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / classification
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Microsomes, Liver / enzymology*
  • Microsomes, Liver / metabolism
  • Perphenazine / metabolism*
  • Recombinant Proteins / antagonists & inhibitors
  • Recombinant Proteins / classification
  • Recombinant Proteins / metabolism
  • Substrate Specificity


  • Antipsychotic Agents
  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • Isoenzymes
  • Recombinant Proteins
  • Cytochrome P-450 Enzyme System
  • Perphenazine