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In the event of overdosage, supportive measures including gastric lavage and emesis should be employed. Substantial overdoses of Astemizole can cause death, cardiac arrest, QT prolongation, cardiac arrest, torsades de pointes, and other ventricular arrhythmias. These events can also occur, although rarely, at doses (20-30 mg) close to the recommended dose (10 mg/daily). (See WARNINGS and DOSAGE AND ADMINISTRATION.)
Seizures and syncope have also been reported with overdose and may be associated with a cardiac event.
Overdose patients should be carefully monitored as long as the QT interval is prolonged or arrhythmias are present. In some cases, this has been up to six days. In overdose cases in which ventricular arrhythmias are associated with significant QT prolongation, treatment with antiarrhythmics known to prolong QT intervals is not recommended.
Astemizole does not appear to be dialyzable.
Oral LD50 values for Astemizole were 2052 mg/kg in mice and 3154 mg/kg in rats. In neonatal rats, the oral LD50 was 905 mg/kg in males and 1235 mg/kg in females.
Concomitant administration of Astemizole with erythromycin is contraindicated because erythromycin is known to impair the cytochrome P450 enzyme system which also influences astemizole metabolism. There have been two reports to date of syncope with Torsades De Pointes, requiring hospitalization, in patients taking combinations of astemizole 10 mg daily with erythromycin. In each case the QT intervals were prolonged beyond 650 milliseconds the time of the event; One patient also received ketoconazole and the other patient also had hypokalemia.
Concomitant administration of astemizole with ketoconazole tablets is contraindicated because available human pharmacokinetic data indicate that oral ketoconazole significantly inhibits the metabolism of astemizole, resulting in elevated plasma levels of astemizole and desmethylastemizole. Data suggest that cardiovascular events are associated with elevation of astemizole and/or astemizole metabolite levels resulting in electrocardiographic QT prolongation.
Concomitant administration with itraconazole is also contraindicated based on the chemical resemblance of itraconazole and ketoconazole. In vitro data suggest that itraconazole has a less pronounced effect on the biotransformation system responsible for the metabolism of astemizole compared to ketoconazole.
Astemizole is contraindicated in patients with known hypersensitivity to astemizole or any of the inactive ingredients.
Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.
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