What should be done if a patient has a QTc interval ≥ 500 msec while on methadone?

If a patient has a QTc interval of 500 msec or greater while on methadone, it is important to discontinue or avoid starting methadone due to the potential risk of serious cardiac complications. Methadone is known to prolong the QTc interval, which can lead to Torsades de Pointes, a life-threatening arrhythmia. A QTc of 500 msec is considered a threshold where the likelihood of significant cardiac risk increases markedly.

In this context, the decision to discontinue or avoid methadone is essential for patient safety. Continuing treatment or simply monitoring the patient without any adjustments does not adequately address the increased risk of serious side effects associated with prolonged QTc, and increasing the dose would further exacerbate this risk. Thus, the safest and most appropriate action in the presence of a significantly prolonged QTc interval is to stop methadone to protect the patient's cardiovascular health.