New guidelines address arrhythmia risk of methadone

23 January 2009

MedWire News: US experts have issued recommendations for arrhythmia screening of patients on methadone treatment, aimed at reducing the incidence of QTc interval prolongation and torsade de pointes.

The guidelines were developed by a multidisciplinary panel of electrophysiologists, epidemiologists, and pain management and substance abuse specialists, headed by Mori Krantz (University of Colorado, Denver, USA). Their goal was to review evidence about adverse effects of methadone on the heart and to develop safety recommendations for doctors prescribing the drug.

They found strong evidence that both oral and intravenous methadone are associated with a dose-dependent increased risk for QTc interval prolongation and torsade de pointes. The incidence of these adverse events and the underlying mechanisms remain unclear.

Accordingly, the panel recommends that clinicians should inform patients of arrhythmia risk when prescribing methadone and ask patients about any history of heart disease, arrhythmia, and syncope.

Krantz et al say that all patients should undergo electrocardiogram (ECG) to measure the QTc interval before treatment, within 30 days of starting treatment, and annually thereafter. If the QTc interval is in the range 450–500 ms, patients should be monitored more frequently, and if it exceeds 500 ms, clinicians should consider discontinuing methadone, reducing the dose, eliminating contributing factors, or using an alternative therapy.

Clinicians should also be aware of interactions between methadone and other drugs that prolong the QT interval or slow methadone elimination.

Writing in the Annals of Internal Medicine, Krantz et al say they believe that increased clinical vigilance will reduce sudden cardiac death among patients receiving methadone in opioid treatment and for chronic pain.

“These recommendations may inform both the product labelling for methadone as well as practice standards for opioid treatment programs,” they add.

Ann Intern Med 2009; Advance online publication