Opioid switching from morphine to methadone causes a minor but not clinically significant increase in QTc time: A prospective 9-month follow-up study.

Case reports and retrospective studies suggest that methadone causes an increase in QTc (QT time corrected for heart rate) time and risk of torsades de pointes arrhythmia. No prospective studies in pain patients have been conducted, and data on whether a methadone-induced increase in QTc time persists during long-term treatment have not been reported. Eight chronic nonmalignant pain patients experiencing insufficient pain control or intolerable side effects during treatment with oral morphine switched to oral methadone and were included in this study. Electrocardiograms were obtained at baseline and at follow-up 2 weeks, and 3 and 9 months after the opioid switch. Start of methadone caused a minor but statistically significant increase in QTc time, while fluctuations in QTc during treatment with stable doses of methadone were neither clinically nor statistically significant. We observed no episodes of arrhythmias.