Arrhythmic Side of Ondansetron Alongside Antiemetic Effect

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To the Editors:
Brenner and Boucher1 reported that patients may have hidden risk factors that, together with ondansetron, could result in a proarrhythmic state that could lead to adverse effects, such as arrhythmias. Administration of ondansetron should be individualized and used cautiously in patients with risk factors for arrhythmia.1
The US Food and Drug Administration currently recommends avoiding use of ondansetron in patients with congenital long QT syndrome because of the risk of torsades de pointes.2 Up to 35% of patients with congenital long QT syndrome have a normal or nondiagnostic resting electrocardiogram, and up to 60% of normal, healthy populations may have a corrected QT interval measuring 410 to 460 millisecond.3 Patient-specific risk factors for drug-induced torsades de pointes are the same factors that are known to be associated with an increase in the QT interval, that is, female sex, bradycardia, hypokalemia, hypomagnesemia, hypocalcemia, diuretic agent use, hypothermia, and history of heart disease.4 Sugrue et al5 reported that the combination of a lead V3–derived corrected QT interval (QTc) and a lead I–derived T-wave right slope discriminated the torsadogenic cases from the nontorsadogenic controls exposed to virtually identical sotalol/dofetilide loads with near 90% accuracy. Consideration of T-wave parameters in addition to the QTc has significant potential to enhance risk stratification in patients.
In this context, considering the association between ondansetron and ventricular arrhythmia to evaluate electrocardiogram screening or continuous monitoring requirement, investigation of relation between new scoring sysytem including parameters such as lead V3–derived QTc, lead I–derived T-wave right slope, female sex, bradycardia, hypokalemia, hypomagnesemia, hypocalcemia, diuretic agent use, hypothermia, and ventricular arrhythmia occurence may shed light on future studies.
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