Tricyclic antidepressants have a narrow therapeutic index and, therefore, become potent cardiovascular and central nervous system toxins in moderate doses.
Complications include effects of prolonged hypotension, cardiac arrhythmias, and seizure. Death results from cardiovascular collapse.
Best markers for suspected overdose are a history of depression, suicidality, and overdose with a sudden deterioration in mental status and vital signs.
At 1 to 2 hours after ingestion, there is a rapid decline in mental and cardiovascular status. Diagnosis established on clinical grounds and classic ECG changes (sinus tachycardia progressing to wide complex tachycardia and ventricular arrhythmias with increasing severity of intoxication).
Hypertonic sodium bicarbonate improves conduction abnormalities and hypotension.
Management of arrhythmias involves correction of acidosis, hypoxia, and electrolyte imbalance. Antiarrhythmic drugs should generally be avoided.
Hypotension usually responds to correction of hypoxia and administration of intravenous fluids and sodium bicarbonate. Treatment with vasopressors (such as norepinephrine) is controversial and should only be done in consultation with a medical toxicologist or intensive care specialist.
Benzodiazepines are the first-line treatment for seizures.
An antidepressant overdose occurs when a person ingests an amount of medication that is more than a reasonable and normal dose.  Tricyclic antidepressants (TCAs) are the main cause of damaging antidepressant overdose because, unlike other antidepressants, they have a narrow therapeutic range and become potent cardiovascular and central nervous system toxins in moderate doses.
Staff Specialist in Emergency Medicine
The Prince Charles Hospital
AN declares that he has no competing interests.
Dr Alastair Newton would like to gratefully acknowledge Dr Catherine Kelly and Dr Robert S. Hoffman, previous contributors to this monograph. CK and RSH declare that they have no competing interests.
The Children's Hospital
EB declares that he has no competing interests.
Consultant Physician and Clinical Toxicologist
National Poisons Information Service (Newcastle)
RT declares that he has no competing interests.
Emeritus Professor of Clinical Pharmacology
University of Edinburgh and Western General Hospital
LP declares that he has no competing interests.
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