Topiramate Utilization After Phentermine/Topiramate Approval for Obesity Management: Risk Minimization in the Era of Drug Repurposing

Introduction The US FDA required a Risk Evaluation and Mitigation Strategy (REMS) for phentermine/topiramate, an anti-obesity medication, to prevent congenital malformations. No REMS is required for single-ingredient topiramate, which may be used off-label for the same purpose. Objective The aim of this study was to evaluate the impact of phentermine/topiramate approval in 2012 on subsequent topiramate use among patients with obesity. Methods We used a national insurance claims database to conduct an interrupted time-series study (2009–2015). Enrollees aged 18–65 years in each examined calendar quarter had full insurance benefits during that quarter and the preceding 6 months. We required patients to have an obesity diagnosis and no other conditions warranting topiramate use. We calculated topiramate or comparator drug (atorvastatin, metformin) initiation rates and evaluated changes in trends before and after 2012 (transition period). Results Among topiramate users, 80% were female, and demographic characteristics remained consistent during the study period. Between 2009 and 2011, the topiramate initiation rate (95% confidence interval) among patients with obesity was 0.85 (0.73–0.98) per 1000 patients, with no significant upward or downward trend. In the first quarter of 2013, this rate had increased more than 2.5-fold (change: + 1.36 [1.19–1.52]). Metformin and atorvastatin initiation rates did not change. Topiramate initiation rates were threefold higher than phentermine/topiramate rates during the post-approval period. Conclusion Phentermine/topiramate approval was associated with increased topiramate use among patients with obesity. Prescribers are encouraged to enhance patient education and monitoring in such clinical use since topiramate prescribing information, compared with REMS for phentermine/topiramate, has less emphasis on preventing prenatal exposure.