Inhibition of alprazolam and desipramine hydroxylation in vitro by paroxetine and fluvoxamine: comparison with other selective serotonin reuptake inhibitor antidepressants

J Clin Psychopharmacol. 1995 Apr;15(2):125-31. doi: 10.1097/00004714-199504000-00008.


In vitro preparations of human liver microsomes were used to study the inhibiting effects of two selective serotonin reuptake inhibitor (SSRI) antidepressants, paroxetine and fluvoxamine, on metabolism via hydroxylation of alprazolam and of desipramine. These reactions are mediated by Cytochromes P450-3A4 and P450-2D6, respectively. Paroxetine was a highly potent inhibitor of desipramine hydroxylation; the inhibition constant (Ki) value of 2.0 microM indicated greater inhibiting potency than fluoxetine or norfluoxetine. The in vitro data predicted in vivo impairment of desipramine clearance by coadministration of paroxetine which was in the same range as observed in a clinical study. Fluvoxamine, by contrast, was a much weaker inhibitor of desipramine hydroxylation, having a Ki value (16.6 microM) similar to those of sertraline and desmethylsertraline. For hydroxylation of alprazolam, paroxetine was a relatively weak inhibitor, approximately comparable to fluoxetine, whereas fluvoxamine showed inhibiting capacity similar to that of norfluoxetine. The in vitro data predicted the degree of impairment of alprazolam clearance observed in vitro model can therefore provide clinically relevant data on prediction of potential drug interactions with SSRIs.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alprazolam / pharmacokinetics*
  • Biotransformation
  • Culture Techniques
  • Cytochrome P-450 CYP2D6
  • Cytochrome P-450 CYP2E1
  • Cytochrome P-450 Enzyme Inhibitors*
  • Cytochrome P-450 Enzyme System / physiology
  • Desipramine / pharmacokinetics*
  • Dose-Response Relationship, Drug
  • Fluvoxamine / pharmacology*
  • Humans
  • Hydroxylation
  • Microsomes, Liver / drug effects*
  • Microsomes, Liver / enzymology
  • Mixed Function Oxygenases / antagonists & inhibitors*
  • Mixed Function Oxygenases / physiology
  • Paroxetine / pharmacology*
  • Selective Serotonin Reuptake Inhibitors / pharmacology*


  • Cytochrome P-450 Enzyme Inhibitors
  • Serotonin Uptake Inhibitors
  • Paroxetine
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • Cytochrome P-450 CYP2E1
  • Cytochrome P-450 CYP2D6
  • Fluvoxamine
  • Desipramine
  • Alprazolam