What is the recommended management of a doxepin overdose?

Management of Doxepin Overdose

For doxepin overdose, immediately initiate cardiac monitoring with ECG, secure the airway, establish IV access, and administer sodium bicarbonate for life-threatening cardiotoxicity (QRS ≥100ms, ventricular arrhythmias, or hypotension), as doxepin is a tricyclic antidepressant that causes sodium channel blockade. 12

Immediate Resuscitation and Monitoring

Initial Assessment and Stabilization

• Obtain ECG immediately and initiate continuous cardiac monitoring - this is non-negotiable 2
• Protect the airway and establish IV access 2
• Monitor for at least 6 hours with cardiac monitoring and observation for CNS/respiratory depression, hypotension, arrhythmias, conduction blocks, and seizures 2
• If ANY signs of toxicity appear during observation, extend monitoring significantly - patients have died from late arrhythmias after inadequate observation 2

Critical ECG Findings

Look specifically for:

• QRS duration ≥100ms (0.10 seconds) - this is the best indicator of overdose severity 1
• Terminal rightward axis deviation in lead aVR 1
• Any ventricular arrhythmias or conduction delays 12

Gastrointestinal Decontamination

All suspected doxepin overdose patients should receive GI decontamination 2:

• Large volume gastric lavage followed by activated charcoal 2
• Secure the airway BEFORE lavage if consciousness is impaired 2
• Never induce emesis - this is contraindicated 2

Cardiovascular Management

Sodium Bicarbonate - First-Line Antidote

Administer hypertonic sodium bicarbonate for life-threatening cardiotoxicity 1:

Adult dosing:

• Initial: 50-150 mEq IV bolus 11
• Maintenance: Prepare 150 mEq/L solution, infuse at 1-3 mL/kg/h 1
• Target serum pH: 7.45-7.55 2

Pediatric dosing:

• Initial: 1-3 mEq/kg 11
• Use 0.5 mEq/mL solution (vs 1 mEq/mL in adults) 1

Indications for sodium bicarbonate:

• QRS ≥100ms 2
• Ventricular arrhythmias 1
• Hypotension 1
• Any life-threatening cardiotoxicity 1

Mechanism: Sodium loading and alkalemia work synergistically - sodium overcomes channel blockade while alkalemia reduces drug binding 1

Hyperventilation as Adjunct

• If pH response to bicarbonate is inadequate, add hyperventilation 2
• Use extreme caution with combined therapy - monitor pH frequently 2
• Avoid pH >7.60 or pCO2 <20 mmHg - this is dangerous 2

Refractory Arrhythmias

If arrhythmias don't respond to sodium bicarbonate/hyperventilation 2:

• Consider lidocaine (Vaughan-Williams class Ib) 1
• Consider bretylium or phenytoin 2
• AVOID Type 1A and 1C antiarrhythmics (quinidine, disopyramide, procainamide) - these are contraindicated 2

Refractory Cardiogenic Shock

VA-ECMO is reasonable for refractory shock from sodium channel blocker poisoning 1 - this has been successfully used in polypharmacy overdoses including doxepin 3

CNS Management

Seizure Control

Use benzodiazepines as first-line 1:

• Diazepam (preferred) or midazolam 1
• If ineffective, use other anticonvulsants (phenobarbital, phenytoin) 2

Critical warning: Seizures are more common with doxepin than other TCAs 4 - a study showed 7.1 times higher odds of seizures with doxepin's close relative dothiepin compared to other TCAs, even after adjusting for dose 4

Airway Management

• Early intubation is advised for CNS depression due to potential for abrupt deterioration 2
• Patients with only minor sedation and normal QRS can still develop major complications 4

Physostigmine

NOT recommended except for life-threatening symptoms unresponsive to other therapies, and only after consulting poison control 2

Antidotes and Adjuncts

Intravenous Lipid Emulsion

May be reasonable for life-threatening sodium channel blocker poisoning refractory to other treatments 1:

• 20% lipid emulsion: 1.5 mL/kg up to 100 mL bolus 1
• Infusion: 0.25 mL/kg/min for up to 30 minutes 1

Flumazenil - CONTRAINDICATED

Do NOT give flumazenil in doxepin overdose 1:

• Flumazenil can precipitate seizures and arrhythmias in the presence of tricyclic antidepressants 11
• This includes supraventricular tachycardia, ventricular arrhythmias, and asystole 1

Monitoring for Complications

Watch for:

• Prolonged toxic coma - doxepin has long pharmacokinetic properties; patients may not regain consciousness for 5-7 days 5
• Anticholinergic effects: severe dry mouth, urinary retention, blurred vision, dilated pupils 2
• Hypotension, tachycardia 2
• Confusion, hallucinations, agitation 2
• Hypothermia or hyperpyrexia 2

Laboratory Monitoring

• Do NOT use plasma drug levels to guide management 2
• Monitor: electrolytes (watch for hypokalemia, hypernatremia, hypochloremia with bicarbonate therapy) 1
• Monitor for metabolic acidosis 2

Ineffective Treatments

The following are NOT effective and should not be used 2:

• Hemodialysis
• Peritoneal dialysis
• Exchange transfusions
• Forced diuresis

Exception: Hemoperfusion may rarely benefit acute refractory cardiovascular instability 2

Post-Resuscitation Care

• Psychiatric evaluation is mandatory - overdose is often deliberate, and patients may attempt suicide by other means during recovery 2
• Continue monitoring until risk of recurrent toxicity is low and vital signs normalized 2

Key Pitfalls to Avoid

1. Inadequate observation period - deaths occur from late arrhythmias in patients who received inadequate monitoring 2
2. Using flumazenil - absolutely contraindicated with TCA co-ingestion 11
3. Ignoring normal QRS - patients with minor sedation and normal QRS can still have seizures and arrhythmias, especially with doxepin 4
4. Delaying sodium bicarbonate - give early for QRS ≥100ms, don't wait for arrhythmias 12
5. Using Type 1A/1C antiarrhythmics - these worsen sodium channel blockade 2