Background and Importance Methadone continues to be the drug of choice in managing opioid withdrawal. However, it is known that its use is related to QT prolongation, torsades de pointes and even sudden cardiac death. The interaction with other drugs could worsen this effect.

Aim and Objectives To quantify the prevalence of methadone drug-drug interactions with risk of QT interval prolongation and the incidence of cardiovascular events during admission.

Material and Methods We conducted a retrospective, descriptive study that included all patients receiving methadone in a tertiary hospital between January 2021 and September 2022.

The variables collected were: age, sex, opioid abuse, treatment with methadone prior to admission, methadone dose, cardiovascular history, number of drugs prescribed -in addition to methadone- likely to prolong QT during admission, and development of cardiovascular complications. Interactions were consulted in Lexicomp

Results A total of 109 patients were collected, the median age of 56 (interquartile range (IQR) 50-60), and 74.3% were male. 82.6% of patients had a history of substance abuse recorded in the electronic medical record, with previous opioid use explicit in 61.5% and were on methadone treatment. Remaining percentage were on methadone for: respiratory weaning (9.3%), analgesia (3.5%) and new managing opioid withdrawal (4.6%). The median methadone dose was 50 mg (IQR 35-80 mg). A total of 9.2% had a history of cardiovascular disease prior to admission.

Patients received a mean of 1.8 QT-prolonging drugs in addition to methadone during admission. In this cohort, 93.6% of patients received any QT-prolonging drug, 48.6% and 21.1% two or three QT-prolonging drugs, respectively. The most frequently prescribed QT-prolonging drugs were quetiapine (24.8%), mirtazapine (19.3%) and ondansetron (12.9%). During admission, 11.0% of patients suffered a cardiovascular event with arrhythmias being the most frequent event (54.6%). A higher proportion of patients with previous cardiovascular history suffered a new cardiovascular event (19.3% vs 7.2%).

Conclusion and Relevance Our results show a high prevalence of patients using methadone concomitant with other drugs likely to prolong QT during admission.

A more significant proportion of patients with a previous history of cardiovascular events suffered a new event during hospitalisation.

Conflict of Interest No conflict of interest