Bradycardia in a carbamazepine overdose: a case report

Objectives: Carbamazepine (CBZ) is an antiepileptic drug used in epilepsy and also in the treatment of neuropatic pain and bipolar disorder. CBZ has quinidine-like effects on cardiac conduction. Bradiarrhythmias or atrioventricular conduction delays have rarely been reported, predominantly in elderly women during chronic therapy (1). Case report: We describe the case of a 66-year old woman admitted to our Toxicology Unit for a self-induced overdose with CBZ. The patient had taken 12 g of extended-release tablets from her husband 3 hours before reaching the hospital.On arrival she presented alert and cooperative, vital parameters were in range. She received oral administration of 50 g of activated charcoal in order to reduce drug absorption. Fluid iv therapy with saline solutions and sodium bicarbonate 1.4% were started and continued for 5 days. A 12-lead ECG showed regular sinus rhythm. Serum CBZ levels were continuously monitored throughout hospitalization. At the 6th post-ingestion hour, vomiting associated with disorientation, facial trismus, upward eye movement and conspicuous mydriasis occurred. Her heart rate dropped to 38 b/m, urging the iv administration of a bolus of 1mEq/kg b.w. sodium bicarbonate and 1 mg atropine which reverted bradycardia in a few minutes. A similar pattern flared after three hours and a third one occurred at the 16th post-ingestion hour. By that time the ECG showed a junctional rhythm with 38 to 42 b/m which tended to recur during the next 24-hour period and monitored for 72 hs. The time course of serum CBZ levels was strictly related to the heart rate decrease. During the following days a continuous 24h-ECG was performed, showing normal rhythm. The patient was transferred to the psychiatric ward on 7th post-ingestion day. Conclusions: The present case shows how monitoring ECG is required especially in elderly women in CBZ overdose, as potential life-threatening bradyarrhythmias or atrioventricular conduction delays may occur either with therapeutic or elevated CBZ serum levels. References: 1. Kasarskis EJ et al. Carbamazepine-induced cardiac dysfunction. Arch Intern Med 1992; 152, 186-191.