Elevated plasma tricyclic levels with therapeutic doses of imipramine

Nine (15%) of 59 patients treated with imipramine at doses of 150 to 300 mg/day had steady-state plasma levels greater than 500 ng/ml. Low capacity for hydroxylation was found in all six patients for whom hydroxy metabolites were measured. Maximum tricyclic levels in the nine study patients were comparable to levels found in tricyclic antidepressant overdoses (651-2439 ng/ml). No study patient experienced any adverse effects: QRS durations were all less than 100 msec, and a mildly dry mouth was the most commonly reported side effect (five of nine patients). Depressive symptoms recurred in three patients when their imipramine dose was decreased.