Severe caffeine poisoning with mexiletine successfully treated by extracorporeal methods

A 20-year-old woman was brought to the hospital in an ambulance after ingesting 18 g of caffeine and 3500 mg of mexiletine 80 min earlier. On arrival at the emergency department, her vital signs were as follows: blood pressure, 65/37 mmHg; heart rate, 140 beats/min; and Glasgow Coma Scale, E4V4M6. Laboratory analyses revealed hypokalemia and lactic acidosis. The patient was treated with mechanical ventilation after intratracheal intubation, intravenous noradrenaline infusion, gastric lavage, and activated charcoal administration. Shortly afterwards, she developed pulseless ventricular tachycardia, and veno-arterial extracorporeal membrane oxygenation (VA-ECMO) was initiated. As the circulatory collapse continued, hemodialysis (HD) was performed with continuous intravenous infusion of noradrenaline. After the completion of HD, the noradrenaline dose was reduced. On hospital day 2, HD was performed on the second day of hospitalization. On hospital days 3 and 4, the patient was weaned off VA-ECMO and ventilator. The blood concentrations of caffeine and mexiletine at presentation were 387 μg/mL and 1.1 μg/mL respectively. During the first HD, blood concentrations of both drugs were markedly reduced.

It has been reported that mexiletine may reduce the clearance of caffeine probably via inhibition of N-demethylation. In this case, the endogenous clearance of caffeine, calculated from blood concentrations, was considerably lower than estimated. If HD had not been performed, it may have taken longer to wean off the VA-ECMO because of reduced caffeine clearance in the presence of mexiletine. Notably, caffeine poisoning is more severe and prolonged when mexiletine is administered.