Tricyclic antidepressant toxicity.

Tricyclic antidepressants are dibenzazepine derivatives with adrenergic, anticholinergic, and direct cardio-depressant activity. Double-blind clinical studies show TCAD to be efficacious for two-thirds of depressed patients. Cardiac toxicity is significant, especially on diseased myocardium. Serious arrhythmias and intracardiac blocks have been reported on therapeutic doses. Tricyclic antidepressant overdose is a serious condition which is becoming progressively more common. The agents' principal toxicities are to the nervous system and the heart. The syndrome can be divided into three stages of varying severity. The vast majority of cases are in the mild Stage I. Some patients reach Stage II with major CNS effects and increasing intracardiac block. Stage III, which encompassed less than 5% of poisonings, is a potentially fatal situation with respiratory arrest, convulsions, and ventricular arrhythmias. Prevention is extremely important in poisoning therapy. Supportive measures are all that is generally needed for mild poisoning. Moderate and severe overdoses will require respiratory support, anticonvulsants, physostigmine, and beta-blockers. Cardioversion and pacing may be necessary.