Lidocaine for diphenhydramine-induced ventricular tachycardia: A case report.

Diphenhydramine overdose can cause life-threatening ventricular dysrhythmias through sodium channel blockade, similar to tricyclic antidepressant (TCA) toxicity. Current management guidelines recommend sodium bicarbonate as first-line therapy, with class Ib antiarrhythmics such as lidocaine considered in refractory cases, though this recommendation is largely extrapolated from TCA data. Clinical reports describing lidocaine use in diphenhydramine toxicity remain exceedingly rare. We report a case where a 16-year-old female who ingested approximately 315 tablets of diphenhydramine and developed pulseless ventricular tachycardia during emergency department resuscitation. Return of spontaneous circulation was achieved after sodium bicarbonate, amiodarone and defibrillation, but recurrent wide-complex tachycardia occurred shortly thereafter. She was treated with a lidocaine bolus and continuous infusion, resulting in progressive QRS narrowing and rhythm stabilization. Diphenhydramine exposure was confirmed with toxicology testing. The lidocaine infusion was weaned, and patient was discharged home without further dysrhythmias. Experimental data demonstrates that diphenhydramine binds preferentially to open sodium channels and dissociates slowly, suggesting a mechanistic basis for lidocaine's therapeutic effect. This case provides additional clinical evidence supporting the use of lidocaine as an adjunct for refractory ventricular dysrhythmias in diphenhydramine induced sodium channel blockade and highlights the important of early recognition and consultation with a poison center in severe antihistamine toxicity.