Clinically Relevant Drug-Drug Interactions in Primary Care

Mary Carpenter, PharmD; Holly Berry, PharmD; Allen L. Pelletier, MD


Am Fam Physician. 2019;99(9):558-564. 

In This Article

Combination of Drugs That Prolong the QTc Interval

QT prolongation syndrome increases the risk of torsades de pointes, a life-threatening arrhythmia. Although torsades de pointes is rare, its severity warrants a discussion of risk factors and the likelihood of occurrence (Table 5).[47] Torsades de pointes is most likely to occur when two or more QT interval–prolonging drugs are administered to a patient who is already at high risk for arrhythmia.[47,48]

Table 6[48–51] includes a list of drugs that may cause QT prolongation. Avoiding the combination of drugs from the highest or moderate risk group is advised, especially in patients with a significant history of cardiac events. If unavoidable, monitoring with electrocardiography soon after initiation and yearly thereafter while continuing concomitant therapy is advised.[49,51] The U.S. Food and Drug Administration guidance regarding QT prolongation defines increases greater than 20 msec as a substantial risk for developing torsades de pointes.[50]