50: The number of patients on >100mg/day of methadone needed to be screened with an EKG to detect 1 person with a QTc >500 ms
A recent review in the Annals of Internal Medicine suggested guidelines for QTc interval screening in methadone users.  The “number needed to treat” was thus calculated from several studies reviewed which show that about 2% of patients on methadone maintenance therapies (at doses >100 mg daily) developed QTc intervals in excess of 500 ms. [1,2]
Torsade de pointes rarely occurs with a QTc of less than 500 ms. Although the relationship between increasing QT interval and risk of developing torsade de pointes is not linear,4 the risk of cardiac events (including syncope and sudden cardiac death) is markedly increased (OR = 4.22) when QTc is greater than 500 ms in patients with congenital long QT syndrome.[1,5,6]
The recent guidelines released in the Annals of Internal Medicine suggest that physicians should discuss potential risks and benefits of methadone therapy in patients with QTc of 450-500. For those with QTc of greater than 500 ms, the guidelines suggest that the physician discuss with the patient either discontinuing the methadone, decreasing the dose, or changing to a different therapeutic agent to treat the Opioid dependence.
1. QTc Interval Screening in Methadone Treatment. M. J. Krantz, J. Martin, B. Stimmel, D. Mehta and M. C.P. Haigney. Ann Intern Med 2009; 387-395 . http://www.annals.org/cgi/reprint/150/6/387.pdf
2. First Do No Harm … Reduction? M. N. Gourevitch. Ann Intern Med 2009; 417-418. http://www.annals.org/cgi/content/full/150/6/417
3. The QT interval. Bednar MM, Harrigan EP, Anziano RJ, Camm AJ, Ruskin JN. Prog Cardiovasc Dis. 2001 Mar-Apr;43(5 Suppl 1):1-45.
4. Drug-induced prolongation of the QT interval. Roden DM. N Engl J Med. 2004;350:1013-22.
5. Phenotypic Variability and Unusual Clinical Severity of Congenital Long-QT Syndrome in a Founder Population. P. Brink, L. Crotti, V. Corfield et al. Circulation 112: 2602-2610.
6. Risk Stratification in the Long-QT Syndrome S. Priori, P. Schwartz, C.Napolitano, et al. N Engl J Med 2003 348: 1866-1874.
Dr. Hall is a 1st year internal medicine resident at NYU Medical Center