Benzydamine N-oxygenation as an index for flavin-containing monooxygenase activity and benzydamine N-demethylation by cytochrome P450 enzymes in liver microsomes from rats, dogs, monkeys, and humans

Drug Metab Pharmacokinet. 2015 Feb;30(1):64-9. doi: 10.1016/j.dmpk.2014.09.006. Epub 2014 Oct 5.


Benzydamine is an anti-inflammatory drug that undergoes flavin-containing monooxygenase (FMO)-dependent metabolism to benzydamine N-oxide; however, benzydamine N-demethylation is also catalyzed by liver microsomes. In this study, benzydamine N-oxygenation and N-demethylation mediated by liver microsomes from rats, dogs, monkeys, and humans were characterized comprehensively. Values of the maximum velocity/Michaelis constant ratio for benzydamine N-oxygenation by liver microsomes from dogs and rats were higher than those from monkeys and humans, despite roughly similar rates of N-demethylation in the four species. Benzydamine N-oxygenation by liver microsomes was extensively suppressed by preheating liver microsomes at 45 °C for 5 min or at 37 °C for 5-10 min without NADPH, and benzydamine N-demethylation was strongly inhibited by 1-aminbobenztriazole. Liver microsomal benzydamine N-oxygenation was inhibited by dimethyl sulfoxide and methimazole, whereas N-demethylation was inhibited by quinidine. High benzydamine N-oxygenation activities of recombinant human FMO1 and FMO3 and human kidney microsomes were observed at pH 8.4, whereas N-demethylation by cytochrome P450 2D6 was faster at pH 7.4. These results suggest that benzydamine N-oxygenation and N-demethylation are mediated by FMO1/3 and P450s, respectively, and that the contribution of FMO to metabolic eliminations of new drug candidates might be underestimated under certain experimental conditions suitable for P450 enzymes.

Keywords: CYP2D6; FMO1; FMO3; NADPH; Preheating of liver microsomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Inflammatory Agents / metabolism*
  • Benzydamine / analogs & derivatives*
  • Benzydamine / metabolism
  • Biotransformation
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • Dogs
  • Humans
  • In Vitro Techniques
  • Macaca fascicularis
  • Male
  • Methylation
  • Microsomes, Liver / enzymology
  • Microsomes, Liver / metabolism*
  • Oxidation-Reduction
  • Oxygenases / genetics
  • Oxygenases / metabolism*
  • Rats, Sprague-Dawley
  • Recombinant Proteins
  • Species Specificity


  • Anti-Inflammatory Agents
  • Recombinant Proteins
  • benzydamine N-oxide
  • Benzydamine
  • Cytochrome P-450 Enzyme System
  • Oxygenases
  • dimethylaniline monooxygenase (N-oxide forming)