QT prolongation and torsades de pointes among methadone users: reports to the FDA spontaneous reporting system.
BACKGROUND
Recent case series have associated the synthetic opioid, methadone, with QT prolongation and torsades de pointes (TdP) ventricular arrhythmia.


OBJECTIVE
To review and analyze adverse events (QT prolongation and TdP) reported to the Food and Drug Administration (FDA) to determine the patient characteristics, dosages of methadone, and outcomes of methadone-treated patients.


METHODS
The study design was a retrieval and retrospective analysis of reports of adverse events associated with methadone voluntarily reported to the FDA MedWatch program from 1969 to October 2002. Reports were accessed via QSCAN (DrugLogic, Reston, VA), a commercially available software interface.


RESULTS
In a total of 5,503 reports of adverse events associated with methadone, 43 (0.78%) noted the occurrence of TdP and 16 (0.29%) QT prolongation. Doses were reported in 42/59 (71%) of cases; mean dose was 410 +/- 349 mg/day (median 345, range 29-1680). The dosages for 10 of the 42 cases (29%) were within the recommended range for methadone maintenance treatment, 60-100 mg/day. Female gender, interacting medications, hypokalemia, hypomagnesemia, and structural heart disease, risk factors previously identified with other drugs known to cause TdP, were found in 44 (75%) cases. Most adverse events required hospitalization or resulted in prolonged hospitalization (28/59, 47%) and 5/59 (8%) were fatal.


CONCLUSIONS
Cases of TdP associated with methadone have been reported to the FDA MedWatch system. Analysis of the cases provides evidence that prolonged QT and TdP can occur over a wide range of dosages including those usually recommended for addiction treatment.
Pearson
Ellen C
EC
University of Arizona Health Sciences Center, Tucson, AZ 85724, USA. pearsone@email.arizona.edu
Woosley
Raymond L
RL
D000293:Adolescent; D000328:Adult; D016907:Adverse Drug Reaction Reporting Systems; D000368:Aged; D016208:Databases, Factual; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000139:chemically induced*; D008297:Male; D008691:Methadone / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D008875:Middle Aged; D009293:Opioid-Related Disorders / Q000534:rehabilitation; D012189:Retrospective Studies; D016171:Torsades de Pointes / Q000139:chemically induced*; D014481:United States; D014486:United States Food and Drug Administration
D008691:Methadone