Dose-dependent kinetics of imipramine in elderly patients.

In a group of elderly depressed patients treated with imipramine (50-200 mg/day), six patients had the dose changed after 1-3 weeks of treatment. In all cases an increased dose resulted in a considerably disproportional rise in the plasma level of the active metabolite desipramine. In a group of elderly depressed patients treated with nortriptyline (40-100 mg/day) the dose/plasma level ratio could be examined in 6 patients, and there was no tendency towards a disproportional rise in plasma level, when the dose was raised. Dose changes, thus, may result in unpredictable changes in plasma levels during imipramine treatment and therapy control by plasma level monitoring may be difficult in these patients. Additional treatment with perphenazine (8-16 mg/day) to patients on imipramine (N = 3) or nortriptyline (N = 2) caused a marked rise in drug levels for imipramine in particular affecting the desipramine levels.