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Peer Reviewed
Objective
Methadone can prolong the QT interval, the time taken from when the cardiac ventricles of the heart start to contract to when they finish relaxing. Methadone is a mixture of R-(laevorotatory) and S-(dextrorotatory) stereoisomers. R-methadone inhibits cardiac potassium channel function less than S-methadone. We tested if switching from methadone to R-methadone would reduce corrected QT (QTc) intervals in methadone maintenance treatment (MMT) patients.
Findings/Key points
In this interventional study with nine MMT patients, removal of S-methadone resulted in a small and not clinically relevant reduction in QTc interval. Consistent with previous reports, this study suggests a risk that supra-therapeutic R-methadone concentrations can cause prolonged QTc intervals.
Design/methods
Nine stabilized MMT patients, using median (range) 70 (40–120) mg methadone, were included. Data (ECG recordings, serum samples, and withdrawal symptoms) were collected both before drug intake (Cmin) and at 3 h after drug intake (Cmax), and were collected on the day before the switch from methadone to equipotent R-methadone dose and at 14 and 28 days after the switch. A cardiologist calculated QTc intervals retrospectively. Serum electrolytes and methadone concentrations were measured.
