Electrocardiogram Abnormalities Following Diphenhydramine Ingestion: A Case Report

Area of Science:

• Toxicology
• Cardiology
• Emergency Medicine

Background:

• Tricyclic antidepressants (TCAs) are frequently prescribed for psychiatric conditions and neuropathic pain.
• TCAs are known to induce characteristic electrocardiogram (ECG) changes during overdose, primarily a dominant terminal R wave in aVR and QRS widening, due to sodium channel blockade.
• Diphenhydramine (Benadryl) shares similar sodium channel-disrupting properties.

Purpose of the Study:

• To report a case of diphenhydramine overdose in a pediatric patient.
• To highlight the diagnostic utility of ECG in identifying sodium channel blockade from diphenhydramine.
• To demonstrate the efficacy of sodium bicarbonate in treating diphenhydramine-induced toxicity.

Main Methods:

• A case report of a 13-year-old female presenting to the ED after a diphenhydramine overdose.
• Clinical assessment including vital signs, symptoms (palpitations, nausea, confusion, agitation, tachycardia, opsoclonus), and ECG.
• Administration of sodium bicarbonate and monitoring of clinical and ECG response.

Main Results:

• The patient's ECG revealed significant terminal R waves in aVR and right axis deviation (large S waves in lead I).
• Following sodium bicarbonate administration, notable improvements in ECG findings and patient symptoms were observed.
• The clinical presentation and ECG changes were consistent with sodium channel blockade.

Conclusions:

• Diphenhydramine, similar to TCAs, can cause life-threatening sodium channel blockade.
• ECG findings, specifically terminal R waves in aVR, are crucial indicators of this toxicity.
• Sodium bicarbonate is an effective antidote for reversing diphenhydramine-induced sodium channel blockade and improving patient outcomes.