Interaction of psychotropic drugs with monoamine oxidase in rat brain

Literature observations indicate that some psychotropic drugs may have inhi bitory activity towards monoamine oxidase (MAO). This study was undertaken to assess the potency, isozyme selectivity and mechanism of inhibition of r epresentative first- and second-generation antidepressant drugs towards rat brain MAO-A and MAO-B. Five tricyclic antidepressants (imipramine, trimipr amine, clomipramine, amitriptyline and doxepine) and three selective seroto nin reuptake inhibitors (fluoxetine, fluvoxamine and citalopram) were exami ned. They showed inhibitory activity towards MAO-A and MAO-B, with clear se lectivity for MAO-B (K-i in the micromolar range). Their mechanism of inhib ition was competitive towards MAO-B and of a mixed competitive type towards MAO-A. The results suggest that some of the drugs examined might also cont ribute an MAO inhibitory effect in chronically treated patients.