Summary — The addition of Limited Use criteria (less restrictive access) for zoledronic acid resulted in an immediate and significant increase in uptake and resulted in differences in patient/physician characteristics. In comparison, the uptake of denosumab (only listed with Limited Use) was rapid. Thus, formulary access restrictions have significant implications for prescribing.
Introduction — The researchers 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 the administrative burden on physicians when prescribing zoledronic acid.
Methods — The researchers identified users of zoledronic acid and denosumab using Ontario pharmacy claims data. The number of new patients and physicians was plotted and examined over time. Interrupted time series analysis examined the impact of a formulary modification to zoledronic acid use and prescribing. Descriptive characteristics of patients and prescribers were summarized pre- and post-formulary modification for zoledronic acid and overall for denosumab.
Results — The researchers identified 1463 zoledronic acid patients treated by 627 physicians and 16,736 denosumab patients treated by 2904 physicians. In the first 2 months on the market, the researchers identified a rapid uptake of denosumab (>450 physicians and >1200 patients) in contrast to zoledronic acid (<10 physicians and <10 patients). Zoledronic acid use increased significantly in the 2-month post-formulary change, yet no change in denosumab was observed. Prior to the formulary modification, more zoledronic acid patients had a history of osteoporosis therapy (41 vs. 26 %) or bone density testing (30 vs. 10 %). Compared to zoledronic patients (post-formulary modification), more denosumab patients had prior osteoporosis therapy (55 vs. 26 %), yet fewer had a gastrointestinal diagnosis (6 vs. 11 %).
Conclusion — The researchers identified a rapid uptake of denosumab in only 15 months of observation. A provincial formulary modification to zoledronic acid resulted in an increase in utilization and impacted patient characteristics.
Drug prescribing behaviour