Methadone may cause potentially fatal arrhythmia, Georgetown researchers find

WASHINGTON, D.C. – Methadone, a drug commonly used to treat patients addicted to narcotics, may, in high dosages or in susceptible individuals, cause a potentially fatal cardiac arrhythmia known as torsades de pointes (TdP), researchers at Georgetown University Medical Center have found. An abstract of their findings will be presented Wednesday, April 4, at the Experimental Biology 2001 annual meeting.

“Because methadone is widely used to treat patients dependent on heroin and other narcotic drugs, and it is not unusual for such patients to have cardiovascular complications, we weren’t sure whether the reported arrhythmias were due to drug addiction or some other factor,” said Raymond L. Woosley, MD, PhD, associate dean of clinical research at Georgetown Medical Center. “However, our data clearly show that methadone has the same pharmacologic actions that are seen with other agents known to cause these arrhythmias.”

In the laboratory, Woosley and his colleagues showed that methadone blocks a key potassium channel in human and animal cells, which, if the same thing occurred in a human heart, could lead to a potentially fatal arrhythmia.

The team’s findings have not yet been confirmed in humans, but their hypothesis about methadone’s role in causing arrhythmias came from anecdotal reports to an international registry that Woosley and his colleagues established to collect cases of cardiac arrhythmias following administration of specific medication(s). The registry website, www.QTdrugs.org, is funded by the General Clinical Research Center (GCRC) and the Center for Education and Research on Therapeutics (CERT) at Georgetown.

Woosley cautioned that patients should not become concerned about these findings and stop taking their methadone. However, if they experience symptoms of dizziness or loss of consciousness they should contact their physician as soon as possible. He also cautioned physicians to be aware of the potential for methadone to induce torsades de pointes because of its ability to block cardiac potassium channels. Woosley and his colleagues now plan to conduct studies in humans to further examine methadone’s potential cardiac effects.

Georgetown University Medical Center includes a biomedical research enterprise as well as the nationally ranked School of Medicine, and the School of Nursing and Health Studies.