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Context: The effect of methadone on corrected QT interval (QTc) in patients with cancer pain is not well-known. Objectives: To describe and characterize the effect of low-, moderate-, and high-dose enteral methadone on QTc interval in patients with cancer. Methods: Retrospective cohort study including patients prescribed enteral methadone during the 27-month study period. Participants were divided into 3 methadone daily dose groups: <30 (low dose), 30 to 59 (moderate dose), ≥60 (high dose) mg. The primary outcome was the incidence of QTc prolongation (>450 ms for females and >430 ms for males). Secondary outcomes included the magnitude of change in QTc after starting methadone, the incidence of clinically significant QTc prolongation (>500 ms) and the prevalence of torsades de pointes and syncope. Results: Two hundred three patients met study inclusion criteria: 91 (45%) low dose, 52 (26%) moderate dose, and 60 (29%) high dose. Incidence of QTc prolongation for low-, moderate-, and high-dose groups was 50 (55%), 37 (71%), and 43 (72%), respectively (P = .039, low vs high dose). Incidence of clinically significant QTc prolongation was 10 (11%), 4 (8%), and 7 (12%) for low-, moderate-, and high-dose groups. For patients without QTc prolongation prior to initiating methadone, 62% of moderate-dose patients and 67% of high-dose patients had QTc prolongation, while taking methadone. Conclusion: This study found a notably high incidence of QTc prolongation in patients with cancer using enteral methadone. Future studies should aim to determine the risk of adverse cardiac effects in the cancer population and determine appropriate monitoring of methadone for pain management. [ABSTRACT FROM AUTHOR]