Tricyclic Antidepressant (TCA) Overdose

What to do right now

1. Call 911 or your local emergency number. Say what was taken, how much, and when.
2. Do not induce vomiting.
3. If the person is unconscious but breathing, place them on their side in the recovery position.
4. If they are not breathing normally, start CPR.
5. If they have a seizure, protect their head and do not put anything in their mouth.
6. Gather all medicine bottles and packaging for the paramedics.
7. Stay with them. If the overdose may have been intentional, remove access to other medicines and means of harm.

Why tricyclics are dangerous in overdose

Tricyclic antidepressants have several actions that, in excess, cause toxicity:

• Sodium channel blockade in the heart: slows electrical conduction (wide QRS on ECG), leading to ventricular arrhythmias.
• Alpha-receptor blockade: widens blood vessels, causing low blood pressure.
• Anticholinergic effects: fast heart rate, dilated pupils, dry hot skin, urinary retention, confusion, see anticholinergic toxicity.
• Effects on brain chemicals: seizures and coma.

The amount needed to cause serious toxicity can be relatively small: as little as 10 to 20 mg/kg in adults, and a few tablets can be dangerous to a toddler.

Symptoms

Early or mild

• drowsiness or agitation
• confusion
• dry mouth, dilated pupils, blurred vision
• flushed, hot, dry skin
• fast heart rate
• urinary retention, reduced bowel sounds

Severe

• seizures
• coma
• low blood pressure and shock
• wide-complex arrhythmias, including ventricular tachycardia
• slowed breathing

Deterioration can be rapid, within an hour of a seemingly mild presentation.

Diagnosis

Diagnosis is based on the history and examination, supported by:

• ECG: QRS widening above 100 ms predicts seizures, and above 160 ms predicts arrhythmias. Other features include a tall R wave in lead aVR and a fast heart rate.
• Continuous heart monitoring.
• Blood tests: blood gas, electrolytes, glucose, kidney function, and acetaminophen and aspirin levels, as people may have taken several substances.
• Drug level testing confirms exposure but does not guide treatment as closely as the ECG.

Treatment

Treatment takes place in an ER and often an intensive care unit, guided by a poison center or medical toxicologist:

• Airway and breathing support, with intubation if consciousness is reduced.
• Activated charcoal if the person presents early and the airway is protected.
• IV sodium bicarbonate: the key treatment for QRS widening, arrhythmias and low blood pressure. It reverses the sodium channel effect.
• IV fluids and vasopressors (such as norepinephrine) for low blood pressure.
• Benzodiazepines for seizures. Phenytoin is avoided.
• Lipid emulsion therapy or extracorporeal support in severe, refractory cases.
• Monitoring for at least 6 hours for people with no symptoms and a normal ECG; longer and in intensive care for others.

Flumazenil and physostigmine are generally avoided because they can provoke seizures or arrhythmias.

Mental health care

Many TCA overdoses are intentional. After medical recovery, a mental health assessment, safety planning and follow-up treatment for depression are essential. Prescribers may choose safer antidepressants, limit supplies, or ask family to help store medicines for people at risk.

Prevention

• store medicines out of reach of children in locked or child-resistant containers
• dispose of unused medicines safely
• prescribers should consider overdose risk and limit quantities for people at risk of suicide
• take medicines exactly as prescribed, and do not combine with alcohol or other sedatives

Frequently asked questions

What are the symptoms of a tricyclic antidepressant overdose?

Symptoms include drowsiness, confusion, dry mouth, dilated pupils, hot dry skin and a fast heart rate. Severe overdoses cause seizures, coma, very low blood pressure and dangerous heart rhythms, sometimes within an hour.

Why are tricyclic antidepressants dangerous in overdose?

They block sodium channels in the heart, slowing its electrical signals and causing life-threatening arrhythmias. They also lower blood pressure and cause seizures. A relatively small number of tablets can be dangerous, especially to children.

How is a TCA overdose treated?

Treatment is in hospital, with breathing support, heart monitoring, IV sodium bicarbonate to reverse heart effects, fluids and medicines for low blood pressure, and benzodiazepines for seizures. Activated charcoal may be given early.

What should I do if someone took too much amitriptyline?

Call 911 or your local emergency number immediately, even if they seem fine. Do not make them vomit. Keep them on their side if drowsy, start CPR if they stop breathing normally, and bring the medicine packaging.