What is the management for a diphenhydramine (Benadryl) overdose?

Management of Diphenhydramine (Benadryl) Overdose

The management of diphenhydramine overdose requires immediate assessment of ABCs (Airway, Breathing, Circulation), establishing IV access, and providing supportive care with cardiac monitoring as the foundation of treatment. 1

Initial Assessment and Stabilization

• Immediately assess ABCs and level of consciousness
• Maintain IV access throughout treatment
• Position patient appropriately:
  • Trendelenburg position for hypotension
  • Sitting up for respiratory distress
  • Recovery position if unconscious
• Administer oxygen as needed
• Call for medical assistance/Poison Control Center (1-800-222-1222) 2

Cardiac Monitoring and Management

• Obtain ECG to assess for QRS prolongation and terminal rightward axis deviation (in lead aVR)
• For life-threatening cardiotoxicity with QRS widening (>0.10 msec):
  • Administer sodium bicarbonate IV bolus (1000 mEq/L in adults, 500 mEq/L in children) 1
  • Consider continuous cardiac monitoring for at least 6 hours after ingestion

Specific Treatments Based on Severity

Mild Symptoms (drowsiness, mild anticholinergic effects)

• Supportive care and observation
• H1 antihistamines are not recommended (would worsen anticholinergic toxicity)

Moderate to Severe Symptoms

• Consider early endotracheal intubation for airway protection in severe cases 1
• For seizures or agitation:
  • Administer benzodiazepines (e.g., lorazepam, diazepam) 3
  • Avoid phenytoin (ineffective for toxin-induced seizures)
• For hypotension unresponsive to fluids:
  • Administer vasopressors (dopamine 2-20 μg/kg/min titrated to increase systolic blood pressure) 4
  • Consider vasopressin (0.01-0.04 U/min) for refractory hypotension 4

Critical Cases

• For refractory cardiac arrest due to severe toxicity:
  • Consider extracorporeal life support (VA-ECMO) 1
• For severe anticholinergic toxicity with life-threatening symptoms:
  • Physostigmine may be considered in hospital setting (not in pre-hospital care) 3, 5
  • Caution: physostigmine is contraindicated if QRS prolongation is present

Gastrointestinal Decontamination

• Do not induce emesis due to risk of rapid CNS depression and seizures 3
• Activated charcoal may be considered if:
  • Patient presents within 1 hour of ingestion
  • Airway is protected or patient is alert with intact gag reflex
  • No contraindications exist

Monitoring and Supportive Care

• Monitor vital signs every 30 minutes initially, then hourly for at least 4-6 hours 4, 1
• Provide close observation for 24 hours after severe reactions 4
• Document the overdose episode including:
  • Pre-treatment assessments
  • Description and grading of symptoms
  • Management provided

Disposition

• Patients with intentional overdose or suicidal intent should be admitted for psychiatric evaluation after medical clearance 3
• Patients with significant symptoms should be admitted for continued monitoring
• Asymptomatic patients who remain stable after 6 hours of observation may be discharged with appropriate follow-up

Special Considerations

• Avoid succinylcholine as a neuromuscular blocker due to potential interactions 1
• Diphenhydramine overdose can present with toxic psychosis and hallucinations that may mimic other conditions 6
• Fatal outcomes have been reported with diphenhydramine levels >19 mg/L in adults 7
• Recent trends show increasing use of diphenhydramine with illicit substances, requiring heightened vigilance 8

Remember that diphenhydramine overdose can rapidly progress from anticholinergic symptoms to life-threatening complications including hyperpyrexia, status epilepticus, coma, and cardiac arrhythmias.