Background: We sought to describe the use of zoledronic acid and denosumab by physicians and patients over time, and examine the impact of a 2012 provincial formulary modification that removed prescribing restrictions for zoledronic acid.
Methods: We identified users of zoledronic acid and denosumab using Ontario pharmacy claims data. The number of new patients and physicians were plotted and examined over time. Interrupted time-series analysis examined the impact of a formulary modification to zoledronic acid. Descriptive characteristics of patients and prescribers were summarised pre- and post-formulary change for zoledronic acid and overall for denosumab.
Results: We identified 1,463 zoledronic acid users treated by 627 physicians and 16,736 denosumab users treated by 2,904 physicians. In the first two months on the market, we identified a rapid uptake of denosumab (>450 new physicians and >1,200 new patients) in contrast to zoledronic acid (<10 new physicians and <10 new patients). Zoledronic acid use increased significantly in the two months post-formulary change with >80 new physicians and >200 new patients. Prior to the formulary change, more zoledronic acid users had a history of osteoporosis therapy (41% vs. 26%) or bone density testing (30% vs. 10%). Compared with zoledronic users initiating after the formulary change, more denosumab users had prior osteoporosis therapy (55% vs. 26%), yet fewer had a gastrointestinal diagnosis (6% vs. 11%).
Conclusion: We identified a rapid uptake of denosumab in only 15 months of observation. A provincial formulary modification removing administrative burden on physicians prescribing zoledronic acid resulted in an increase in utilisation and impacted patient characteristics.
Disclosure: The authors declared no competing interests.