Factors Affecting Usage Levels and Trends of Innovative Oncology Drugs Upon and After Reimbursement Under Taiwan National Health Insurance: Interrupted Time Series Analysis

Healthcare expenditure on pharmaceuticals, especially innovative oncology drugs, is escalating. Current knowledge on this topic is largely limited to studies conducted upon reimbursement of new drugs. We investigated how endogenous factors (e.g., changed reimbursement criteria, such as an expanded indication) and exogenous factors (e.g., competing drugs) affect the level and trends of innovative oncology drug utilization in the Taiwan National Health Insurance (NHI) system, both upon reimbursement and afterward. This retrospective longitudinal study analyzed monthly data (January 2009 to December 2014) from the NHI Research Database on the consumption (prescribing volume) of 15 innovative oncology drugs reimbursed by the NHI between 2007 and 2013. Effects of endogenous and exogenous factors on drug utilization were evaluated using interrupted time series analyses. In segmented regression analyses, changed drug prescribing volume after the indication expanded (endogenous factor) was statistically significant; however, drug volume did not change significantly after prescription restrictions changed. First‐competitors and non‐first‐competitors (exogenous factors) were significantly associated with drug prescription levels or utilization rates. Taking sorafenib as an example, the post‐reimbursement drug prescribing volume did not change significantly after its therapy line changed (endogenous factor), whereas the reimbursement of first‐competitors (exogenous factor) was significantly associated with a lower level or usage rate of sorafenib. Utilization of innovative oncology drugs in Taiwan changed dramatically after NHI reimbursement, driven largely by expanded indications and new competitors. Drug utilization evaluations should investigate both endogenous and exogenous factors.