Effectiveness of risedronate and alendronate on nonvertebral fractures: an observational study through 2 years of therapy.

This observational study showed that after 2 years, both risedronate and alendronate lowered the risk of hip and nonvertebral fractures compared with patients filling in a single bisphosphonate prescription. Post hoc analyses of the placebo-controlled trials suggested earlier effects for risedronate (6-12 months) than for alendronate (18-24 months). The present study extends our 1-year observational data that confirmed an earlier fracture reduction with risedronate and evaluated the absolute and relative effectiveness of alendronate and risedronate in clinical practice over 2 years. We observed three cohorts of women aged 65 years and older who initiated once-a-week dosing of bisphosphonate therapy; (1) patients adherent to alendronate (n = 21,615), (2) patients adherent to risedronate (n = 12,215), or (3) patients filling only a single bisphosphonate prescription (n = 5,390) as a referent population. Proportional hazard modeling compared the incidence of hip and nonvertebral fractures among the cohorts over 2 years after the initial prescription. In this cohort, we previously showed at 12 months a significant reduction of hip and nonvertebral fractures with risedronate but not with alendronate. At the end of 2 years, the cumulative incidence of hip fractures in the referent cohort was 1.9 %, and incidence of nonvertebral fractures was 6.3 %. Relative to the referent, 6 months after initiating therapy and continuing through 2 years, both risedronate and alendronate cohorts had approximately a 45 % lower incidence of hip fractures and a 30 % lower incidence of nonvertebral fractures. These observations suggest that both risedronate and alendronate are effective at reducing the risk of hip and nonvertebral fracture after 2 years of treatment and support the post hoc analyses of placebo-controlled trials indicating an earlier effect of risedronate.