Methadone-Associated Prolongation of the QTc Interval at Doses Used for Chronic Pain.

Purpose: Methadone HCl is used for the management of opioid addiction and chronic pain. Published reports indicate that methadone can be associated with a prolonged corrected QT (QTc) interval, especially at daily doses greater than 100 mg. The risk of this adverse effect is not always considered by health care pain specialists, who sometimes use lower doses. The objectives of this case series were to evaluate the effects of methadone on the QTc interval in patients being treated for chronic pain and to determine whether there was a correlation between dosing and the degree of QTc prolongation.
Methods: A computerized list was generated for patients who had active methadone prescriptions between December 2007 and November 2008. We performed a retrospective chart review to evaluate methadone dosing, potential drug interactions, electrocardiograms (ECGs), and the QTc interval. An emphasis was placed on patients with QTc intervals greater than 500 milliseconds (msec).
Results: Of the 51 patients reviewed, seven had QTc intervals greater than 500 msec. Methadone doses ranged from 5 to 180 mg/day; three patients received daily doses greater than 100 mg. Six of the seven patients were taking at least one other drug that had the ability to prolong the QTc interval.
Conclusion: Our case series suggested that QTc intervals should be routinely monitored in patients receiving methadone and that patients should be screened before therapy is initiated. Ideally, the QTc interval should be monitored before treatment begins and during repeated intervals thereafter. On the basis of the analysis, a protocol was developed at our facility for monitoring ECGs in patients being treated with methadone for chronic pain.