A 24-year-old opioid use disorder patient on stable methadone maintenance presents with QTc of 540 ms on ECG. The most appropriate management step is:

• A Add IV magnesium sulfate empirically and continue methadone
• B Reduce or discontinue methadone and consider switching to buprenorphine ✓
• C Add amiodarone to suppress ventricular ectopy
• D Ignore if asymptomatic; methadone does not cause torsades de pointes

Explanation

Methadone is a well-established QTc-prolonging agent that blocks cardiac hERG potassium channels, predisposing to torsades de pointes (TdP), a potentially lethal arrhythmia. A QTc exceeding 500 ms substantially raises TdP risk; the threshold for clinical concern is generally QTc > 450 ms in men and > 470 ms in women. At a QTc of 540 ms, the most appropriate clinical decision is to reduce or taper methadone and transition to buprenorphine, which has no significant QTc effect. Amiodarone itself prolongs QTc and is contraindicated in this context.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.