Prolongation of the corrected QT interval (QTc) has a potential risk of inducing life-threatening cardiac dysrhythmia. Although 5-HT₃ antagonists are useful antiemetics, several cases of cardiac dysrhythmia after administration of 5-HT₃ antagonists have been reported. Therefore, this study was conducted to evaluate the changes in QTc interval that occur after administration of a clinical dose of ondansetron during general anesthesia.

Seventy-five patients, who underwent elective surgery under standardized general anesthesia were evaluated. After anesthetic induction, the patients were given either normal saline, 2 mg or 4 mg of iv ondansetron. The QTc on the electrocardiogram was measured immediately prior to administration of the treatment drug and then every minute after injection of the study drug for 10 minutes, 12 and 15 minutes.

There were no differences observed in the baseline QTc of the different treatment groups. In addition, there were no significant changes in the QTc interval of the control group, however, the QTc interval was prolonged significantly in both the ondansetron 2 mg and 4 mg groups. Further, ΔQTc (the difference in QTc interval from the baseline value) was significantly prolonged in the ondansetron 2 mg and 4 mg groups when compared with the control group. There were no differences in the number of patients who showed abnormal QTc and there were no incidences of dysrhythmia in any of the three groups.

Ondansetron administration for emesis prophylaxis during general anesthesia was associated with statistically significant prolongation of the QTc interval. The authors recommend that caution be used when ondansetron is administered to prevent and/or treat postoperative nausea and vomiting, particularly in patients who have a prolonged QTc interval.