Methadone and QTc Prolongation — MRCPsych Paper B MCQ

Correct answer: E — Reduce methadone, correct reversible factors, seek specialist advice, and consider transfer to buprenorphine

Explanation lettering: E = shown as A · A = shown as B · D = shown as C · C = shown as D · B = shown as E

B is correct. A confirmed QTc above 500 ms represents a clinically important increase in the risk of torsades de pointes and requires active risk reduction. Methadone should be reviewed and reduced, while reversible contributors are sought and corrected, including hypokalaemia, hypomagnesaemia, interacting medicines and other QT-prolonging drugs. Specialist addiction and cardiology input is appropriate, and a planned transfer to buprenorphine should be considered because it has substantially less effect on QTc. Merely repeating the ECG while continuing the same dose, as in A or C, does not adequately address a QTc of 520 ms. Amiodarone can itself prolong QT and is not prophylactic treatment. Abruptly stopping opioid substitution without an alternative risks withdrawal, relapse and overdose; any reduction or transfer should therefore be clinically managed.

Reference: UK Government, Part 3: supporting service users to get the most out of opioid substitution treatment—Cardiac issues, 2021. https://www.gov.uk/government/publications/opioid-substitution-treatment-guide-for-keyworkers/part-3-supporting-service-users-to-get-the-most-out-of-opioid-substitution-treatment-ost