A comparative double-blind controlled study of trimipramine and amitriptyline in major depression: lack of correlation with 5-hydroxytryptamine reuptake blockade.

Thirty-four hospitalized patients with major depression were enrolled in a 3-week double-blind parallel comparative study of trimipramine and amitriptyline. Following a 1-week washout period, patients randomly received one of the two drugs up to 100 mg twice daily on a fixed increment dosage schedule. Both treatments produced a rapid significant clinical improvement that occurred in a predominantly linear fashion. The pattern of improvement was very similar with both drugs. There was no significant correlation between plasma levels of trimipramine and desmethyl-trimipramine and clinical improvement. A negative correlation between amitriptyline plasma levels and clinical improvement was found, whereas a positive correlation occurred with the nortriptyline levels. Amitriptyline, and to a lesser extent trimipramine, prolonged intracardiac conduction. In the amitriptyline group only, this effect was accompanied by significant increases of heart rate and blood pressure. Platelet serotonin content was decreased by 57% by the amitriptyline treatment but remained unchanged in the trimipramine group. This finding constitutes the first clinical evidence that trimipramine does not exert its antidepressant effect through 5-hydroxytryptamine reuptake blockade. It is proposed that neuronal sensitization to 5-hydroxytryptamine might mediate the therapeutic effect of tricyclic antidepressant drugs.