INTRODUCTION: Serious cardiac arrhythmias caused by QT-prolonging drugs are difficult to predict based on physiological measurement and pre-approval clinical trials . Post-marketing surveillance and monitoring are important to generate safety data .

OBJECTIVES: To assess whether an observational study using Medicare claims data can detect the arrhythmogenic risk of QT-prolonging drugs .

METHODS: We identified 17 QT-prolonging drugs with known risk of torsades des pointes (TdP) that were not used to treat cardiac arrhythmias . Amoxicillin and four serotonin-norepinephrine reuptake inhibitors (SNRIs) were used as controls . De-identified claims data of 1.2 million Medicare beneficiaries were accessed . Two separate Cox regressions were done for short-term and chronic-use drugs . The primary outcome was a composite of ventricular arrhythmias and/or sudden death, identified by ICD diagnostic codes . We explored the independent effect of each study drug on the outcomes . Other covariates included patient demographics, comorbidities, and known risk factors for drug-induced cardiac arrhythmia .

RESULTS: We were able to detect increased risk in 14 of 17 study drugs (82.3 %), and none of the control drugs . Among the fluoroquinolones, ciprofloxacin was the safest . Azithromycin and clarithromycin were relatively safe compared to erythromycin . Compared to SNRIs, both citalopram and escitalopram had increased risk, more so with escitalopram than citalopram . Comorbidities associated with increased risk included ischemic heart disease, electrolyte imbalance, bradycardia, acute myocardial infarction, heart failure, and chronic kidney and liver disease .

CONCLUSION: Medicare data can be utilized for post-marketing surveillance and monitoring of the proarrhythmic risk of QT-prolonging drugs in older adults.