Plasma concentrations of tricyclic antidepressants in clinical practice

Plasma concentrations of four tricyclic antidepressant drugs were monitored in 180 patients. Plasma concentrations incongruent with dose suggested noncompliance at some time among 20% of the patients. Plasma concentrations correlated poorly with dose except with amitriptyline. Plasma concentration of drug and active metabolite, in the case of imipramine and amitriptyline, tended to be higher in ng/ml than the daily dose in mg; the converse was true for nortriptyline and desipramine. Most patients achieved "therapeutic"plasma concentrations at doses of 150 mg/day. However, "therapeutic" plasma concentrations did not correlate well with clinical response.