What is the treatment for a patient who has taken an overdose of Benadryl (diphenhydramine)?

Treatment of Diphenhydramine (Benadryl) Overdose

Immediate supportive care with airway management, benzodiazepines for seizures, and sodium bicarbonate for cardiac toxicity are the cornerstones of diphenhydramine overdose treatment—there is no specific antidote. 1

Initial Assessment and Stabilization

Stop any ongoing diphenhydramine administration immediately and assess airway, breathing, and circulation (ABCs). 1 Diphenhydramine overdose presents with anticholinergic toxicity affecting multiple organ systems, including potentially life-threatening cardiac effects due to sodium channel blockade. 1, 2

• Establish intravenous access and administer supplemental oxygen as needed 1
• Monitor vital signs continuously, including cardiac rhythm 1
• Position the patient appropriately to maintain airway patency 1

Cardiovascular Management

For QRS prolongation (>0.10 msec) or wide-complex dysrhythmias, administer sodium bicarbonate 1-2 mEq/kg IV bolus immediately. 1, 3 Diphenhydramine acts as a sodium channel blocker and can cause cardiac toxicity similar to tricyclic antidepressants, making this intervention critical. 1

• For hypotension unresponsive to IV fluid resuscitation, administer vasopressors such as dopamine or vasopressin 1
• Continuous cardiac monitoring is essential as cardiac conduction abnormalities and hemodynamic compromise can progress rapidly 2

Neurological Management

For seizures or severe agitation, administer benzodiazepines as first-line therapy. 1, 3 This is a critical intervention as seizures are a common and potentially fatal complication of diphenhydramine overdose. 2

• Benzodiazepines may be administered by EMS personnel if authorized by medical direction 3
• Avoid physostigmine in the prehospital setting—it should be reserved for hospital administration only 3

Decontamination Considerations

Do not induce emesis or administer activated charcoal en route to the emergency department. 3 Because diphenhydramine can cause rapid loss of consciousness or seizures, these interventions pose significant aspiration risk. 3

• If the patient is already in the emergency department and presents within 1-2 hours of ingestion without altered mental status, activated charcoal may be considered under controlled conditions 4
• For chronic dermal exposures, perform skin decontamination with water or soap and water unless moderate to severe symptoms are already present 3

Supportive Care

Administer IV fluids for volume resuscitation and maintain close observation. 1 The mainstay of treatment remains supportive care while the drug is metabolized and excreted. 4

• Monitor for respiratory depression, particularly if other sedatives were co-ingested 5, 6
• Observe for anticholinergic symptoms including altered consciousness, tachycardia, hyperthermia, urinary retention, and mydriasis 1, 3

Observation and Disposition

Patients with any symptoms beyond mild drowsiness require emergency department evaluation. 3 Specific concerning symptoms include:

• Agitation, staring spells, or inconsolable crying 3
• Hallucinations or abnormal muscle movements 3
• Loss of consciousness, seizures, or respiratory depression 3

For asymptomatic patients, if more than 4 hours have elapsed since ingestion, emergency department referral is not necessary. 3 However, patients should be instructed to call back if symptoms develop, with poison center follow-up at approximately 4 hours post-ingestion. 3

Dose-Based Triage

Children under 6 years who ingest ≥7.5 mg/kg of diphenhydramine require emergency department evaluation. 3

Patients 6 years and older who ingest ≥7.5 mg/kg or 300 mg (whichever is less) require emergency department evaluation. 3

Critical Pitfalls to Avoid

• Never delay basic life support measures (airway, breathing, circulation) while attempting other interventions 1, 4
• Avoid neuromuscular blockers metabolized by cholinesterase in patients with anticholinergic toxicity 1
• Do not underestimate the cardiac toxicity potential—diphenhydramine can cause fatal cardiac conduction abnormalities and hemodynamic collapse 2, 6
• Transport via ambulance should be strongly considered based on patient condition and distance to the emergency department 3