Tricyclic Antidepressant Overdose — Sodium Bicarbonate Protocol

Key Points

• TCAs cause life-threatening sodium-channel blockade in addition to anticholinergic and alpha-blocking effects.
• An immediate ECG is more useful for acute risk stratification than a serum TCA concentration.
• QRS widening, hypotension, ventricular dysrhythmia, seizure, and acidemia are major danger signs.
• Sodium bicarbonate is first-line therapy for life-threatening TCA cardiotoxicity.
• Avoid hypoventilation and acidemia because both worsen sodium-channel blockade.
• Benzodiazepines are first-line treatment for TCA-associated seizures.
• Norepinephrine is commonly used when hypotension persists despite sodium bicarbonate and appropriate volume management.
• Refractory cardiogenic shock from a reversible overdose is an important indication to consider VA-ECMO.

Algorithm

1. Assess airway, breathing, circulation, mental status, and obtain an immediate 12-lead ECG with continuous monitoring.
2. Check glucose, electrolytes, blood gas, acetaminophen concentration, and targeted coingestant studies.
3. If seizure occurs, give a benzodiazepine immediately and correct hypoxemia or acidosis.
4. If QRS is significantly widened, hypotension is present, or ventricular dysrhythmia occurs, administer hypertonic sodium bicarbonate.
5. Repeat bicarbonate according to ECG and hemodynamic response while monitoring pH, sodium, potassium, and chloride.
6. If intubation is needed, avoid post-intubation hypoventilation and maintain controlled alkalemia.
7. Use norepinephrine for persistent shock after bicarbonate and appropriate fluid assessment.
8. Consider lidocaine for refractory ventricular dysrhythmia after adequate bicarbonate therapy with toxicology input.
9. Escalate refractory cardiogenic shock or arrest to an ECMO-capable center when feasible.
10. Continue monitored observation until ECG, mental status, blood pressure, and acid-base status remain stable without rescue therapy.

Clinical Synopsis & Reasoning

Tricyclic antidepressant poisoning is a high-risk overdose because severe neurotoxicity and cardiotoxicity can develop quickly and may be disproportionate to the initial appearance of the patient. TCAs inhibit fast cardiac sodium channels and also have antimuscarinic, alpha-adrenergic blocking, antihistamine, and other ion-channel effects. The resulting syndrome can include tachycardia, dry skin and mucosa, mydriasis, urinary retention, delirium, seizures, coma, hypotension, QRS widening, ventricular tachycardia, and cardiac arrest. Acidemia worsens sodium-channel blockade and increases the unbound fraction of many TCAs, so prevention and correction of hypoventilation and acidosis are central to treatment.

The ECG is the most useful rapid risk-stratification tool. QRS prolongation reflects sodium-channel blockade; a QRS above approximately 100 ms is associated with increased seizure risk, and marked widening above approximately 160 ms has historically been associated with ventricular dysrhythmias. A terminal rightward axis in lead aVR, such as a prominent terminal R wave, also supports sodium-channel toxicity. These thresholds are not absolute, and treatment should be driven by the total clinical picture, including hypotension, ventricular ectopy, worsening QRS duration, and acid-base status. Serum TCA concentrations do not correlate well enough with acute cardiotoxicity to guide emergency treatment.

The differential includes other sodium-channel blockers such as diphenhydramine, carbamazepine, flecainide, propafenone, cocaine, and selected antipsychotics. Mixed overdoses are common. Check for acetaminophen and other occult coingestants when the ingestion is intentional or uncertain. Seizures can abruptly worsen acidosis and cardiotoxicity, so they require immediate benzodiazepine therapy. A patient who initially looks only mildly anticholinergic can deteriorate rapidly, making continuous cardiac monitoring essential when a clinically significant ingestion is suspected.

Treatment Strategy & Disposition

Stabilize the airway, ventilation, and circulation while obtaining an immediate 12-lead ECG and establishing continuous cardiac monitoring. Avoid hypoxemia and acidemia. If intubation is required, preoxygenate carefully and maintain adequate minute ventilation so that abrupt post-intubation respiratory acidosis does not intensify sodium-channel blockade. Treat seizures promptly with benzodiazepines. Activated charcoal can be considered after a potentially serious recent ingestion when the airway is protected and gastrointestinal risk is acceptable, but decontamination must never delay cardiopulmonary stabilization.

Sodium bicarbonate is the primary antidotal therapy for life-threatening TCA cardiotoxicity. The 2025 American Heart Association resuscitation guideline lists an initial adult hypertonic sodium bicarbonate dose of 50 to 150 mEq and a pediatric dose of 1 to 3 mEq/kg, repeated and titrated to control critical manifestations. Indications include significant QRS widening, hypotension from sodium-channel blockade, ventricular dysrhythmia, and cardiac arrest. Sodium loading and alkalinization both contribute to benefit. Follow the ECG, blood pressure, pH, sodium, potassium, and chloride closely. Expert guidance generally avoids serum pH above about 7.55 and sodium above about 155 mEq/L. Once the initial response is achieved, additional boluses or an infusion can be used according to recurrence and local toxicology protocol; the AHA table describes a 150 mEq/L solution infused at 1 to 3 mL/kg per hour.

If hypotension persists after bicarbonate and appropriate volume assessment, norepinephrine is commonly used because alpha blockade contributes to shock. Refractory ventricular dysrhythmias despite adequate alkalinization may respond to lidocaine, a class Ib agent, with toxicology consultation. Avoid class Ia and Ic antiarrhythmics because they worsen sodium-channel blockade, and avoid routine use of physostigmine in cardiotoxic TCA poisoning because bradyarrhythmia and asystole are concerns. Intravenous lipid emulsion has uncertain benefit and is generally reserved for life-threatening toxicity refractory to standard measures when recommended by a medical toxicologist. VA-ECMO is reasonable for refractory cardiogenic shock or persistent malignant dysrhythmia when a reversible poisoning is otherwise likely to recover. Patients with significant ECG abnormalities, seizures, hypotension, altered consciousness, or need for bicarbonate require monitored admission, usually intensive care.

Epidemiology / Risk Factors

• TCAs are prescribed less commonly than many newer antidepressants but remain disproportionately dangerous in overdose.
• Intentional ingestion and mixed-drug overdose are common clinical settings.
• Amitriptyline, nortriptyline, imipramine, desipramine, and clomipramine are representative agents with important cardiotoxic potential.
• Children can develop severe toxicity from relatively small absolute doses because of lower body mass.
• Delayed gastric emptying from anticholinergic effects can prolong absorption after a large ingestion.
• Cardiovascular collapse and seizure are the major mechanisms of early death in severe poisoning.

Investigations

ECG Risk Markers

Pharmacology

Prognosis / Complications

• Patients who remain clinically well with a normal ECG through an appropriate observation period have a low risk of later major TCA cardiotoxicity.
• Early sodium bicarbonate treatment can rapidly narrow the QRS and improve blood pressure in sodium-channel-mediated toxicity.
• Severe acidemia, recurrent seizures, refractory hypotension, ventricular dysrhythmias, and cardiac arrest indicate high risk.
• Because the toxicity is reversible as the drug redistributes and is metabolized, aggressive temporary circulatory support can result in good neurologic recovery in selected refractory cases.
• Persistent conduction abnormalities or hemodynamic instability require ICU-level monitoring until they resolve.
• Psychiatric assessment and suicide-prevention planning are essential after intentional overdose.

Patient Education / Counseling

• Store TCAs securely because even a limited number of tablets can be dangerous to children or other household members.
• Patients prescribed TCAs should understand the danger of taking extra doses and the need to seek emergency care after an overdose.
• After intentional poisoning, address access to medications, mental-health treatment, and a safe discharge plan.
• Warn against combining TCAs with other sedatives or cardiotoxic medications without medical guidance.
• Family members should call emergency services for seizure, collapse, severe confusion, or suspected substantial ingestion rather than inducing vomiting.
• Medication reconciliation should confirm whether the TCA remains the safest long-term therapy after an overdose event.

Notes

The key intervention in TCA poisoning is not simply correction of a laboratory pH. Hypertonic sodium bicarbonate is used because both sodium loading and alkalinization reduce the physiologic consequences of fast sodium-channel blockade. ECG narrowing, blood-pressure improvement, and suppression of ventricular dysrhythmia are meaningful treatment endpoints.

The 2025 AHA special-circumstances guideline recommends sodium bicarbonate for life-threatening cardiotoxicity from tricyclic and tetracyclic antidepressants. The guideline also cautions against extreme alkalemia and hypernatremia, citing expert targets that keep serum pH no higher than about 7.55 and sodium no higher than about 155 mEq/L.

Airway management deserves special attention. A patient with severe poisoning can deteriorate when sedated and intubated if minute ventilation falls and pH drops. When intubation is necessary, the clinician should preserve adequate ventilation and continue antidotal therapy rather than accepting a transient respiratory acidosis.

References

1. American Heart Association 2025 Special Circumstances of Resuscitation: Sodium Channel Blocker Poisoning — Link