Bisphosphonate prescribing, persistence and cumulative exposure in Ontario, Canada

Summary We studied new users of oral bisphosphonates and found that less than half persisted with therapy for 2 years, and interruptions in use were common. During a median observation period of 4.7 years, 10% of patients filled only a single prescription, 37% switched therapies and median cumulative exposure was 2.2 years. Introduction We sought to describe bisphosphonate pre- scribing, persistence and cumulative exposure among seniors in Ontario, Canada. Methods We used Ontario Drug Benefit pharmacy claims to identify residents aged≥66 years who initiated oral bisphosphonate therapy between April 1996 and March 2009. The first date of bisphosphonate dispensing was considered the index date. Persistence with therapy was defined as continuous treatment with no interruption exceeding 60 days. We examined persistence with therapy and the number of extended gaps (>60 days) between prescriptions over time periods ranging from 1 to 9 years. We also identified the proportion of patients filling only a single prescription and switching to a different bisphosph- onate, and calculated the median days of exposure irrespective of gaps in therapy. Results A total of 451,113 eligible new bisphosphonate users wereidentified: meanage=75.6years (SD=6.9),84% female, and median follow-up length=4.7 years. Persistence with therapy declined from 63% at 1 year to 46% at 2 years and 12%at9years.Amongthosewithatleast5yearsoffollow-up (n=213,029), 61% had one or more extended gaps in bisphosphonate therapy. Overall, 10% of patients filled only a single prescription, 37% switched to a different bisphosph- onate and the median exposure was 2.2 years.