Drug-drug interactions contributing to QT prolongation in cardiac intensive care units

Purpose: To determine the most common drug-drug interaction (DDI) pairs contributing to QTc prolongation in cardiac intensive care units (ICUs). Materials and Methods: This retrospective evaluation included patients who were admitted to the cardiac ICUs between January 2009 and July 2009 aged >= 18 years with electrocardiographic evidence of a QTc >= 500 ms. Patients receiving at least two concomitant drugs known to prolong the QT interval were considered to experience a pharmacodynamic DDI. Drugs causing CYP450 inhibition of the metabolism of QT prolonging medications were considered to cause pharmacokinetic DDIs. The causality between drug and QTc prolongation was evaluated with an objective scale. Results: One hundred eighty-seven patients experienced QT prolongation out of a total of 501 patients (37%) admitted during the study period. Forty-three percent and 47% of patients experienced 133 and 179 temporally-related pharmacodynamic and pharmacokinetic interactions, respectively. The most common medications related to these DDIs were ondansetron, amiodarone, metronidazole, and haloperidol. Conclusion: DDIs may be a significant cause of QT prolongation in cardiac ICUs. These data can be used to educate clinicians on safe medication use. Computerized clinical decision support could be applied to aid in the detection of these events. (c) 2013 Elsevier Inc. All rights reserved.