MONDAY, June 26 (HealthDay News) -- Intravenous drug users who receive methadone maintenance therapy to curb their habit are at an increased risk for developing long QT syndrome, according to a report in the June 26 Archives of Internal Medicine.
In vitro, methadone inhibits the cardiac ion channel KCNH2 and prolongs the QT interval, but whether this occurs in patients remains unknown. Jules A. Desmeules, M.D., from Geneva University Hospital in Switzerland, and colleagues addressed this question by retrospectively comparing electrocardiographs from 167 active and former IV drug users receiving methadone maintenance therapy and 80 injection drug users who were not.
The investigators found that 16.2 percent of patients on methadone therapy showed QT interval prolongation of 0.5 seconds or longer compared with none of the control subjects. QT interval prolongation was weakly but significantly linked to methadone daily dose and six patients in the methadone group presented with torsades de pointes.
"QT interval prolongation in methadone maintenance patients hospitalized in a tertiary care center is a frequent finding," the authors write. "Methadone dose, presence of cytochrome P-450 3A4 inhibitors, potassium level, and liver function contribute to QT prolongation."
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