Adoption of once-monthly oral bisphosphonates and the impact on adherence

The extent of the adoption of once-monthly bisphosphonates into general clinical practice is not known, nor is it known if the novel formulation improves adherence.

We analyzed administrative claims 2003-2006 from a large employer-based health insurance database for incident use of oral bisphosphonates and stratified users by daily, weekly, and monthly dosing regimen. We measured adherence as the medication possession ratio (MPR) during the first year of therapy. We compared patient characteristics by dosing regimen and evaluated how the dosing regimen influenced the MPR.

We identified 61,125 incident users of bisphosphonates (n=1034 daily, n=56,925 weekly, n=3166 monthly). Monthly bisphosphonate users were, on average, slightly older than the other groups (mean age 66 years for monthly users vs 65 years for weekly users or 66 years for daily users, P<.05) and more often lived in the North Central or South United States (76% vs 72% weekly users or 69% daily users, P<.05). There were no detectable differences among the dosing groups in the history of serious gastrointestinal risk, comorbidity burden, or prior osteoporotic fractures. During the first year of bisphosphonate therapy, 49% of monthly users had MPR> or =80% compared with 49% of weekly users (not significant) or 23% of daily users (P<.0001).

We found little evidence of preferential prescribing of monthly bisphosphonates to certain types of patients. Furthermore, we found no evidence of improved bisphosphonate adherence with monthly dosing relative to weekly dosing, although adherence with either weekly or monthly dosing was significantly better than with daily dosing.