What are the immediate safety precautions for an adolescent child with a diphenhydramine (Benadryl) overdose?

Immediate Safety Precautions for Adolescent Diphenhydramine Overdose

For an adolescent with diphenhydramine overdose, immediately call 911 and transport to the emergency department via ambulance—do not attempt home management, as serious toxicity including seizures, cardiac arrhythmias, and death can occur unpredictably. 1

Critical Initial Actions

Immediate Emergency Response

• All patients with suspected intentional overdose (including suicidal intent or intentional abuse) must be referred to an emergency department immediately 1
• Transport via ambulance should be strongly considered based on the patient's condition and distance to the hospital 1
• Contact Poison Control (1-800-222-1222) immediately for expert guidance while awaiting EMS 2

Do NOT Attempt These Interventions at Home

• Do not induce vomiting 1
• Do not administer activated charcoal at home or en route to the hospital due to the risk of sudden loss of consciousness or seizures 1
• Do not delay transport to attempt any home decontamination measures 1

Monitoring for Life-Threatening Symptoms

Symptoms Requiring Immediate Emergency Department Referral

Any of the following warrant immediate transport 1:

• Changes in behavior beyond mild drowsiness: agitation, staring spells, hallucinations, or inconsolable crying 1
• Abnormal muscle movements or seizures 1, 3
• Loss of consciousness or severe sedation 1
• Respiratory depression 1
• Cardiac symptoms: chest pain, palpitations, or irregular heartbeat 3

High-Risk Clinical Features

Adolescents are at particular risk for fatal anaphylaxis and may engage in risky behaviors, deny symptoms, or fail to recognize triggers 2. In diphenhydramine overdose specifically, the following signs indicate severe toxicity 3:

• QRS prolongation (>120 ms) on cardiac monitoring 3
• Acidemia (pH <7.2) 3
• Elevated anion gap (>20) 3

Dose-Based Risk Assessment

Toxic Dose Thresholds

• Patients 6 years and older who ingest ≥7.5 mg/kg OR ≥300 mg (whichever is less) should be referred to an emergency department 1
• For context: therapeutic dosing is 1-2 mg/kg per dose with a maximum of 50 mg 4, so overdoses often involve significantly higher amounts

Time-Based Observation

• If the patient has no symptoms and more than 4 hours have elapsed since ingestion, emergency department referral may not be necessary—however, this applies only to clearly sub-toxic doses in unintentional exposures 1
• For adolescents with intentional ingestions, this time-based rule does NOT apply—they must be evaluated regardless of time elapsed 1

Common Toxicity Manifestations

Anticholinergic Effects (Most Common)

The most frequently reported adverse events in diphenhydramine overdose include 5:

• Tachycardia (53.4% of cases) 5
• Hallucinations (46.5% of cases) 5
• Agitation (33.9% of cases) 5
• Somnolence (34.7% of cases) 5
• Mydriasis (dilated pupils, 26.3% of cases) 5

Serious Complications

• Seizures occur in approximately 11.6% of diphenhydramine overdoses 5, 3
• Cardiac arrest has been reported even with therapeutic dosing when administered intravenously 6
• Ventricular dysrhythmias can occur, particularly with QRS prolongation 3
• Death is rare (0.2% in one large series) but has occurred, often in the context of very large ingestions 5

Critical Safety Pitfalls to Avoid

Do Not Delay Transport

• Patients and caregivers are often reluctant to seek emergency care, incorrectly thinking the episode is mild or relying on spontaneous recovery from previous episodes 2
• Diphenhydramine toxicity can progress rapidly and unpredictably—symptoms may worsen suddenly even after initial mild presentation 1

Recognize Intentional Misuse

• Diphenhydramine is frequently misused recreationally for its antihistaminergic and antimuscarinic effects 3
• Adolescents may intentionally ingest large amounts for psychoactive effects 3
• Self-harm ingestions are associated with higher rates of intubation 3

Avoid Physostigmine Outside Hospital Setting

• Physostigmine (an antidote for anticholinergic toxicity) should be reserved for administration in a hospital setting only 1
• EMS personnel should not administer physostigmine en route 1

EMS/Advanced Care Considerations

Interventions EMS May Perform (If Authorized)

• Benzodiazepines may be administered for agitation or seizures if authorized by EMS medical direction 1
• Intravenous sodium bicarbonate may be given if QRS widening (>0.10 msec) is present and authorized by medical direction 1

Cardiac Monitoring

• Continuous cardiac monitoring is essential during transport 2
• Monitor for QRS prolongation, which is strongly associated with severe outcomes 3

Special Considerations for Adolescents

Psychosocial Assessment Required

• All intentional ingestions require psychiatric evaluation in addition to medical management 1
• Adolescents with self-harm intent must be kept in a safe environment and not left alone 1

Co-Ingestions Common

• Diphenhydramine is often involved in polysubstance overdoses 3
• Elicit information about other substances that may have been ingested 1

The key message: diphenhydramine overdose in adolescents is a medical emergency requiring immediate emergency department evaluation and should never be managed at home, regardless of apparent symptom severity at presentation. 1