Astemizole

Astemizole is a nonsedating, long-acting antihistamine widely used in the treatment of allergic rhinitis, allergic conjunctivitis, urticaria and chronic vertigo. Cardiotoxic effects, primarily ventricular abnormalities and torsades de pointes, have been reported in adolescents and adults following astemizole overdose. Wiley and associates report five cases in which significant cardiotoxic effects occurred in children who had received an overdose with astemizole.

The first case involved a four-year-old boy who had ingested 30 mg of astemizole (1.7 mg per kg). Four hours after the overdose, the child became transiently lethargic and was brought to the emergency department. The heart rate was 52 beats per minute (occasionally dropping to 40 beats per minute), blood pressure was 85/37 mm Hg, respiratory rate was 24 breaths per minute and temperature was 36.5[degrees]C (97.7[degrees]F). Oxygen saturation by pulse oximetry was 98 percent in room air. The serum astemizole level obtained four and one-half hours after ingestion was 14 ng per mL (reference laboratory value: 0.4 ng per mL in patients receiving normal daily dosing).

The initial electrocardiogram revealed bradycardia with second-degree atrioventricular block, prolonged QT interval, ventricular bigeminy and ventricular conduction delay with right bundle-branch block. An electrocardiogram obtained on the next day showed first-degree heart block with occasional premature ventricular beats and a corrected QT interval of 0.55 (normal value: less than 0.43). At discharge 72 hours after presentation, the electrocardiogram was normal.

The table summarizes the findings in the five cases reported. One child had stable ventricular tachycardia five hours after ingestion. All of the children had prolonged corrected QT measurements that required one to three days to resolve.

The authors recommend that children who ingest an overdose of astemizole receive emergent medical evaluation, gastric emptying and oral administration of activated charcoal and cathartic. Evaluation should include a 12-lead electrocardiogram with calculation of corrected QT interval and continuous cardiac monitoring over 24 hours. (Journal of Pediatrics, May 1992, vol. 120, p. 799.)

COPYRIGHT 1992 American Academy of Family Physicians
COPYRIGHT 2004 Gale Group