Relationship between age and tricyclic antidepressant plasma levels.

Older depressed patients treated with imipramine or amitriptyline developed higher steady-state plasma levels of imipramine, desipramine, and amitriptyline. In imipramine-treated patients this finding was associated with a decreased rate of drug elimination from plasma. These findings provide at least a partial explanation for the increased susceptibility of the older patient to tricyclic antidepressant side effects and also provide a pharmacological rationale for use of lower dosages in this age group.