Tricyclic Antidepressant Toxicity

TCA toxicity is a life-threatening poisoning driven by sodium channel blockade, anticholinergic effects, and alpha-adrenergic blockade. The primary cause of death is cardiovascular collapse from wide-complex arrhythmias and myocardial depression.[1-2] Toxicity develops rapidly, and the ECG — particularly QRS duration and R wave in aVR — is the most important prognostic tool.[1][3]

1. History

• Which TCA was ingested (amitriptyline, nortriptyline, desipramine, imipramine, doxepin, etc.)? Desipramine has a higher death rate in overdose compared to other TCAs[4]
• Dose ingested: Toxic range ~5–20 mg/kg; however, reported dose is neither reliable nor a good predictor of outcome[1]
• Time of ingestion: Critical for decontamination decisions and anticipating clinical trajectory
• Intentional vs. accidental: Multiple drug ingestion (including alcohol) is common in deliberate TCA overdose[2][5]
• Co-ingestants: Ask specifically about alcohol, benzodiazepines, other sedatives, opioids, other anticholinergics
• Formulation: Immediate-release vs. sustained-release; pill count if available
• Symptoms since ingestion: Drowsiness, confusion, palpitations, seizures, dry mouth, blurred vision
• Vomiting: Spontaneous emesis may have occurred but induced emesis is contraindicated[2]

2. Alarm Features

• QRS ≥100 ms — best single indicator of overdose severity; predicts seizures and ventricular arrhythmias[1][6]
• R wave in aVR >3 mm — good predictive value for seizures or arrhythmias[1]
• Seizures — may herald cardiovascular collapse
• Ventricular dysrhythmias (VT/VF) or Brugada-like pattern on ECG[1]
• Refractory hypotension (SBP <90 mmHg, MAP <65 mmHg)[7]
• Coma or rapidly declining GCS — early intubation advised due to potential for abrupt deterioration[8]
• Cardiac arrest — most deaths occur prehospital or within the first few hours[1]
• Late fatal dysrhythmias have been reported in patients with clinical evidence of significant poisoning who received inadequate GI decontamination[2-3]

3. Medications

Cornerstone treatment

• Sodium bicarbonate (NaHCO₃): 1–2 mmol/kg IV bolus; repeat as needed up to max 6 mmol/kg. Target pH 7.45–7.55; do not exceed pH 7.55–7.60 or Na >155 mEq/L[7][9-11]
• Benzodiazepines: First-line for seizures[1-2]

Second-line agents

• Lidocaine: For wide-complex tachycardia refractory to sodium bicarbonate (class Ib antiarrhythmic competes for sodium channel binding)[10-11]
• Phenytoin/phenobarbital: Alternative anticonvulsants if benzodiazepines fail[2]
• Norepinephrine/vasopressors: For refractory hypotension after fluid resuscitation

Rescue therapies

• Intravenous lipid emulsion (ILE): Recommended after failure of standard therapies for life-threatening toxicity, particularly if VA-ECMO is unavailable; not first-line. Dose: 1.5 mL/kg bolus of 20% lipid emulsion, followed by 0.25 mL/kg/min infusion[10-12]
• VA-ECMO: For refractory cardiogenic shock/cardiac arrest[10-11]

Contraindicated medications

• Type 1A antiarrhythmics (quinidine, procainamide, disopyramide) — absolutely contraindicated[2][6]
• Type 1C antiarrhythmics (flecainide, propafenone) — contraindicated[6]
• Physostigmine — not recommended except for life-threatening anticholinergic symptoms unresponsive to all other therapies, and only in consultation with poison control[2]
• Flumazenil — avoid if co-ingestion with benzodiazepines suspected (may precipitate seizures)
• Induced emesis — contraindicated[2]

4. Diet

• NPO in acute setting; aspiration risk is high given altered mental status and anticholinergic ileus
• No specific dietary triggers or long-term dietary management relevant to acute toxicity

5. Review of Systems

• Neuro: Altered mental status, agitation, delirium, drowsiness, coma, seizures, myoclonus, hyperreflexia, muscle rigidity[1-2]
• Cardiac: Palpitations, chest pain, syncope
• GI: Nausea, vomiting, abdominal distension (ileus from anticholinergic effects)
• GU: Urinary retention[1]
• Skin: Dry, flushed skin; hyperthermia[1]
• Eyes: Blurred vision, mydriasis[2]
• Psych: Hallucinations, confusion, agitation[2]

6. Collateral History and Family History

• Collateral is critical: Determine pill bottles, pill counts, suicide note, access to medications
• Confirm prescription holder (patient vs. family member — especially important in pediatric ingestions)
• Psychiatric history: Prior suicide attempts, current stressors, recent medication changes
• Family history is less relevant in acute toxicity but may inform psychiatric risk assessment
• Children are more sensitive than adults to acute TCA overdose; any amount in infants/young children must be considered serious and potentially fatal[13]

7. Risk Factors

• Psychiatric illness (depression, anxiety) — TCAs prescribed for these conditions; deliberate self-harm is common
• Access to large quantities of TCAs (e.g., new prescription, multiple refills)
• Pediatric patients — accidental ingestion; higher sensitivity to toxicity[13]
• Elderly patients — lower therapeutic doses, higher susceptibility to cardiac and anticholinergic effects
• Co-ingestion with alcohol, sedatives, or other cardiotoxic drugs
• Pre-existing cardiac conduction disease — increased risk of fatal arrhythmia
• Hepatic impairment — impaired TCA metabolism

8. Differential Diagnosis

• Other sodium channel blocker overdose: Cocaine, local anesthetics, class Ia/Ic antiarrhythmics, carbamazepine, propranolol[10-11]
• Anticholinergic toxidrome from other agents: Antihistamines (diphenhydramine), antipsychotics, atropine, jimsonweed
• Serotonin syndrome: If co-ingested with serotonergic agents (clonus, hyperreflexia, diaphoresis — note: diaphoresis distinguishes from pure anticholinergic toxidrome)
• Neuroleptic malignant syndrome: Rigidity, hyperthermia, altered mental status
• Sympathomimetic toxidrome: Cocaine, amphetamines (diaphoresis present, unlike anticholinergic)
• Hyperkalemia: Can cause QRS widening — check potassium
• Brugada syndrome: TCA can unmask Brugada pattern on ECG[1]
• Key distinguishing feature: The combination of anticholinergic signs + QRS widening + sinus tachycardia + rightward terminal axis is highly specific for TCA toxicity[3]

9. Past Medical History

• Psychiatric diagnoses and prior overdose attempts
• Cardiac history (baseline conduction abnormalities, heart failure)
• Seizure disorder
• Hepatic or renal disease
• Current medications (especially other QT/QRS-prolonging drugs, MAOIs, serotonergic agents)
• Prior TCA use and dosing

10. Physical Exam

Vital signs

• Tachycardia (sinus, often >120 bpm) — from anticholinergic and alpha-adrenergic effects
• Hypotension — from alpha blockade and myocardial depression
• Hyperthermia — anticholinergic impairment of sweating
• Tachypnea or respiratory depression depending on severity
• Focused exam (anticholinergic toxidrome — "hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter"):
• Pupils: Mydriasis (dilated, poorly reactive)[2]
• Skin: Dry, flushed, warm[1]
• Mucous membranes: Dry
• Abdomen: Decreased bowel sounds, distension (ileus)[1]
• Bladder: Distended (urinary retention)[1]
• Neuro: Altered mental status (agitation → obtundation → coma), hyperreflexia, myoclonus, muscle rigidity, seizures[1-2]

11. Lab Studies

• ABG/VBG: Assess pH (acidosis worsens toxicity by increasing free drug); guide bicarbonate therapy[10]
• BMP: Sodium (monitor during NaHCO₃ therapy, do not exceed 155 mEq/L), potassium (hypokalemia from alkalinization), glucose, renal function[11]
• Serum lactate: Marker of tissue hypoperfusion
• Urine drug screen: Qualitative TCA screen (note: false positives with carbamazepine, cyclobenzaprine, quetiapine, diphenhydramine)
• Serum TCA levels: Not useful for guiding management — ECG findings are more predictive than serum concentrations[1][6]
• Acetaminophen and salicylate levels: Rule out common co-ingestants in deliberate overdose
• Ethanol level
• CBC, LFTs, coagulation studies: Baseline
• Serial potassium and calcium: Monitor during bicarbonate therapy (hypokalemia, hypocalcemia are adverse effects)[1][11]

12. Imaging

• Chest X-ray: If intubated, or to evaluate for aspiration pneumonia or pulmonary edema[2]
• KUB: Rarely helpful; TCAs are not radiopaque
• CT head: Consider if altered mental status is disproportionate to expected toxicity or if trauma suspected
• Imaging is generally not the priority — ECG and clinical monitoring take precedence

13. Special Tests

• Poison Control Center consultation — recommended for all TCA overdoses[2][5]
• Urine TCA immunoassay: Qualitative confirmation (high false-positive rate; does not change management)
• Activated charcoal: 1 g/kg if presenting within 1–2 hours of ingestion and airway is protected[2][6]
• Gastric lavage: Considered if early presentation with large ingestion and airway secured; emesis is contraindicated[2]

14. ECG

• The ECG is the single most important prognostic and monitoring tool in TCA toxicity.[1][6]

Key findings

• Sinus tachycardia — often the earliest finding (anticholinergic)
• QRS prolongation ≥100 ms — best indicator of severity; associated with seizures[1][6]
• QRS ≥160 ms — associated with ventricular arrhythmias
• Terminal R wave in aVR >3 mm — highly predictive of seizures and arrhythmias; reflects rightward terminal axis deviation[1][4]
• Rightward axis shift of terminal 40 ms of QRS — recognized by terminal S wave in leads I and aVL, R wave in aVR[4]
• Brugada-like pattern (right bundle branch block with ST elevation in V1–V3)[1]
• Prolonged QT interval[3]
• Ventricular tachycardia / ventricular fibrillation — the lethal arrhythmias
• AV conduction blocks[1]
• Monitoring: Continuous cardiac monitoring; serial 12-lead ECGs to track QRS duration response to therapy[3][9]

15. Assessment

• TCA toxicity produces a triad of toxicity: (1) anticholinergic effects, (2) cardiovascular sodium channel blockade, and (3) CNS depression/seizures.[1] Severity stratification is primarily ECG-based:
• Mild: Sinus tachycardia, anticholinergic symptoms, QRS <100 ms
• Moderate: QRS 100–160 ms, altered mental status, hypotension responsive to fluids
• Severe: QRS ≥160 ms, seizures, ventricular arrhythmias, refractory hypotension, coma, cardiac arrest
• Toxicity develops rapidly — patients can deteriorate from alert to cardiac arrest within minutes.[2] Most deaths occur prehospital or in the first few hours.[1] Dual therapy with sodium bicarbonate and mechanical hyperventilation achieves alkalinization targets more effectively and narrows QRS twice as fast as either alone.[9]

16. Treatment Plan

Initial stabilization (ABCs)

• Airway protection — early intubation for CNS depression (abrupt deterioration is possible)[8]
• IV access, continuous cardiac monitoring, 12-lead ECG

GI decontamination

• Activated charcoal (1 g/kg) if within 1–2 hours and airway protected[2][6]
• Emesis is contraindicated[2]
• Sodium bicarbonate protocol (for QRS ≥100 ms, hypotension, arrhythmias, or seizures):
• Bolus: 1–2 mEq/kg (mmol/kg) IV push; may repeat every 3–5 minutes[7]
• Target pH: 7.45–7.55[6][10]
• Max dose: 6 mmol/kg total[7][9]
• Max sodium: Do not exceed 155 mEq/L[10]
• Adjunct: Mechanical hyperventilation (PCO₂ ~30–35 mmHg) synergistically improves alkalinization and QRS narrowing[7][9]
• Monitor and correct hypokalemia and hypocalcemia during therapy[1][11]

Seizure management

• Benzodiazepines first-line (lorazepam 0.1 mg/kg IV or diazepam)[1-2]
• Phenobarbital or phenytoin if refractory[2]

Refractory arrhythmias

• Lidocaine for wide-complex tachycardia unresponsive to NaHCO₃[10-11]
• Avoid class Ia/Ic antiarrhythmics[6]

Refractory hypotension

• IV fluid boluses → norepinephrine
• Consider ILE (20% Intralipid: 1.5 mL/kg bolus, then 0.25 mL/kg/min) if standard therapies fail[10-11]
• VA-ECMO for refractory cardiogenic shock or cardiac arrest[10-11]

17. Disposition

• All suspected TCA overdoses require hospital monitoring[2][5]
• Minimum 6 hours of cardiac monitoring with observation for CNS depression, respiratory depression, hypotension, arrhythmias, conduction blocks, and seizures[2-3]
• If any signs of toxicity during observation → extended monitoring required (typically ICU)[2]
• ICU admission criteria: QRS ≥100 ms, seizures, arrhythmias, hypotension, altered mental status, need for NaHCO₃ therapy or intubation
• Asymptomatic with normal ECG at 6 hours → may be medically cleared for psychiatric evaluation if intentional ingestion
• Poison Control Center consultation recommended for all cases[2]
• Psychiatric consultation — since overdose is often deliberate, patients may attempt suicide by other means during recovery[2]

18. Follow Up / Return Precautions

• Psychiatric follow-up is essential — patients may reattempt suicide during recovery phase[2]
• Restrict access to TCAs and other lethal medications upon discharge
• Return precautions: Seek immediate care for palpitations, chest pain, syncope, seizures, confusion, or recurrent suicidal ideation
• Expected recovery: With appropriate treatment, most patients who survive the first 24 hours recover fully; cardiac toxicity typically resolves within 24–48 hours
• Late dysrhythmias: Rare but reported — patients with significant initial toxicity should have extended monitoring[2-3]
• Medication reconciliation: Consider switching to a safer antidepressant (e.g., SSRI) in consultation with psychiatry

References

1. Extracorporeal Treatment for Tricyclic Antidepressant Poisoning: Recommendations from the EXTRIP Workgroup. — Yates C, Galvao T, Sowinski KM, et al. Seminars in Dialysis. 2014.

2. FDA Drug Label. — Updated date: 2026-01-07. Food and Drug Administration.

3. FDA Drug Label. — Updated date: 2025-11-03. Food and Drug Administration.

4. FDA Drug Label. — Updated date: 2025-07-03. Food and Drug Administration.

5. FDA Drug Label. — Updated date: 2025-12-30. Food and Drug Administration.

6. FDA Drug Label. — Updated date: 2024-12-04. Food and Drug Administration.

7. Common Pitfalls in the Use of Hypertonic Sodium Bicarbonate for Cardiac Toxic Drug Poisonings. — Chan BS, Buckley NA. Clinical Toxicology. 2024.

8. FDA Drug Label. — Updated date: 2023-03-17. Food and Drug Administration.

9. Optimising Alkalinisation and Its Effect on QRS Narrowing in Tricyclic Antidepressant Poisoning. — Pai K, Buckley NA, Isoardi KZ, et al. British Journal of Clinical Pharmacology. 2022.

10. Part 10: Adult and Pediatric Special Circumstances of Resuscitation: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Cao D, Arens AM, Chow SL, et al. Circulation. 2025.

11. 2023 American Heart Association Focused Update on the Management of Patients With Cardiac Arrest or Life-Threatening Toxicity Due to Poisoning: An Update to the American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Lavonas EJ, Akpunonu PD, Arens AM, et al. Circulation. 2023.

12. Lipid Emulsion Treatment for Drug Toxicity Caused by Nonlocal Anesthetic Drugs in Pediatric Patients: A Narrative Review. — Lee SH, Kim S, Sohn JT. Pediatric Emergency Care. 2023.

13. FDA Drug Label. — Updated date: 2023-12-15. Food and Drug Administration.