Outpatient Co-prescription of Ondansetron With Other QT-Prolonging Drugs in a Large Community-Based Health System: A Warning Ignored

Abstract

Introduction: Ondansetron is a 5HT-3 serotonin receptor antagonist that is commonly used to treat nausea and vomiting. The FDA has warned of QT-prolonging effects of ondansetron, especially when combined with other QT-prolonging drugs, or in patients with known cardiac disease. Electronic medical records with warning systems for drug-drug interactions have been promoted for patient safety. We present a review of de-identified data from a large community-based health system to determine how providers responded to electronic warnings when prescribing ondansetron combined with other QT-prolonging drugs. Methods: All prescriptions for ondansetron in combination with QT-prolonging drugs at NorthShore University HealthSystem between January and March 2016 were included in the initial database as part of a quality improvement project. Inpatient orders and IV ondansetron orders were removed. The name and class of co-prescribed QT-prolonging drugs, warning severity, response to the warning by prescribing practitioner (over-ride warning and prescribe, or cancel order), reason for the warning over-ride, patient age and gender were evaluated. Results: There were a total of 9203 episodes of co-prescription of ondansetron and another QT-prolonging drug in 2739 adult patients during the study time period. After filtering, there were 770 outpatient co-prescriptions in 500 patients. Mean patient age was 46.2 years (range 18 to 90 years). Orders were for 592 females (76.8%) and 178 males (33.2%). All warnings were considered “major interactions”. Most orders, 651 (84.5%) prescriptions were administered, while only 119 (15.5%) orders were canceled. The most common classes of co-prescribed QT-prolonging drugs were macrolide antibiotics (40.0%), flouroquinolone antibiotics (17.0%), SARI antidepressants (13.4%), and SSRI antidepressants (9.9%), (Table 1). There were nine (1.4%) cases of co-prescriptions with antiarrhythmic drugs (amioderone and flecainide). The most commonly co-prescribed QT-prolonging medications were azithromycin, levofloxacin, and trazadone (Table 2). Reasons for warning overrides were “benefit outweighs risk” in 266 (40.8%) and “not clinically significant” in 116 cases (17.7%).Table: Table. Classes of Drugs Co-Prescribed with OndansentronTable: Table. List of Drugs Co-Prescribed with OndansetronConclusion: After viewing warnings, practitioners still prescribed ondansetron with other QT-prolonging drugs 85% of the time. This form of co-prescription with ondansetron neglects FDA recommendations and could put patients at risk for cardiac arrhythmias.