Aust. N.Z. J. Med. (1974), 4, pp. 479-484 zy Catecholamine Levels in Tricyclic Antidepressant Self-Poisoning R. Schwarz* and M. Eslert zyxwvutsr From the Department of Psvchiatry, Canberra Hospital, and The Department of Clinical Science, John Curtin School of Medical Research, Australian National University, Canberra. Summary: In a consecutive series of zyxwv 208 patients with tricyclic antidepressant self - poisoning, urinary catec holami ne excretion was measured, and the cate- cholamine level compared with that in ten patients having taken an overdose of other drugs. In both patient groups the electrocardiograph was monitored con- tinuously for a minimum of 48 hours to detect cardiac arrhythmias. Urinary nor- adrenaline excretion was elevated during the first 24 hours after tricyclic anti- depressant self-poisoning, to! a level 2-3 times that found in the other overdose group, but was normal by the third day. Cardiac tachya rr h yt hmias developed i n four of the patients with antidepressant overdosage. The findings support the concept that sympathetic nervous system overactivity underlies the cardiac tachy- arrhythmias which commonly accom- pany self-poisoning with this class of drugs. zyxwvutsr There have been many reports during the last ten years of self-poisoning with tricyclic anti- depressants1* 2. This class of drug is commonly involved in drug overdosage admissions to Australian hospitals3* 4. There is substantial associated mortality, averaging 10-15 % in re- ported series. Toxic reactions noted include cardiac tachyarrhythmias and conduction dis- *Registrar in Psychiatry; Currently Resident in Psychiatry, Ypsilanti State Hospital, Ypsilanti, Michigan U.S.A. tResearch Associate; Currently Fellow in Hypertension, Department of Internal Medicine, University Hospital, Ann Arbor, Michigan U.S.A. zyxwvutsrqpon Correspondence: Dr. M. D. Esler Hypertension Section Department of Internal Medicine University of Michigan Medical Center Ann Arbor, Michigan 48104 U. S. A. Accepted for publication : 29 May, 1974. turbances, hypotension, convulsions, hyper- pyrexia, and respiratory depression2* st 4. The pharmacological basis of the cardiac disturbances is not completely clear. The anti- cholinergic activity of tricyclic antidepressants6 may possibly contribute to the development of tachyarrhythmias2. A second possibility is that the disturbances of cardiac rhythm may be catecholamine-related. The major mechanism of inactivation of noradrenaline at sympathetic nerves, and of clearance of noradrenaline from plasma, is by reuptake into the sympathetic nerve endings6. Tricyclic antidepressants inhibit this process of noradrenaline reuptake'. The concept that disturbed sympathetic nervous system function may possibly underlie the development of cardiac arrhythmias with tricyclic antidepressant self-poisoninghas recent- ly been stressed*. This possibility has been investigated in the present study. Urinary cate- cholamine excretion has been measured serially in patients with tricyclic antidepressant self- poisoning, and the catecholaminelevel compared with that in patients having taken an overdose of other drugs, the latter patients serving as a control population. Within the tricyclic anti- depressant group, catecholamine levels in patients who did, and did not develop cardiac tachyarrhythmias have been compared. Patients and Methods zyxwv Patients and Experimental Protocol The patients in the tricyclic antidepressant group con- stituted a consecutive series of 20 patients admitted to hospital after having taken an overdose of more than 250 mg of amitryptyline, imipramine or a related tricyclic antidepressant drug. Patients in whom one or more additional drugs (including alcohol) were known to also have been taken were excluded from the study. Admission was initially to the intensive care unit, where all patients were confined for a minimum of 48 hours. A physical and neurological examination was given on admission, and a 12-lead electrocardiogram taken. Patients subsequently received regular intensive care unit nursing and medical