1222 Co-Prescription of Ondansetron With Other QT-Prolonging Drugs: Data From a Large Community-Based Hospital System

Abstract

INTRODUCTION: The Food and Drug Administration (FDA) has warned about the co-prescription of ondansetron with other QT-prolonging medications. Electronic medical records (EMR) with built-in warning systems for drug-drug interactions (DDIs) are designed to improve patient safety. However, overriding of warnings are common. Response to warnings for potentially life-threatening DDIs such as QT-prolongation has not been fully investigated. We studied outpatient co-prescription of ondansetron with other QT-prolonging medications in a large community-based health practice. METHODS: Data for all outpatient prescriptions for oral ondansetron from January 1 to March 31st, 2016 at NorthShore University HealthSystem was reviewed. A de-identified dataset was developed that included all outpatient prescriptions for oral ondansetron in patients receiving another QT-prolonging drug. Duplicate orders were removed. Interaction warnings, including the severity of the interactions are generated at the time of order placement. Prescriber response to DDI warnings and further analysis of the co-prescribed QT-prolonging drugs was performed. Demographic information was also studied. RESULTS: 11,935 cases of inpatient and outpatient co-prescriptions of ondansetron with and one or more QT-prolonging drug occurred during the study period. After filtering, there were 884 outpatient ondansetron and QT-prolonging co-prescription orders in 723 patients. All warnings were “severe interactions”. Only 93 (10.5%) prescriptions in outpatients were canceled, while 791 (89.5%) of the prescription orders were overridden. The most common classes of QT-prolonging medications taken by patients with overridden orders for ondansetron were selective serotonin reuptake inhibitors (SSRIs) (33%), macrolide antibiotics (29%), fluoroquinolone antibiotics (13%), and serotonin antagonist reuptake inhibitors (SARIs) (11%) (See Table 1). The most commonly co-prescribed QT prolonging drugs are listed in Table 2. Twelve patients receiving QT-prolonging antiarrhythmic agents had completed orders for ondansetron. 617 (78%) of overridden prescriptions occurred in women. CONCLUSION: Warnings for ondansetron co-prescription with other QT-prolonging drugs are usually ignored. Co-prescription of ondansetron with other QT-prolonging drugs is more common in female patients. This is of particular concern because women are more likely to develop serious arrhythmias related to ondansetron-induced QT-prolongation.