This study examined patients' risk profiles and adherence to treatment in relation to the effect of
risedronate and
raloxifene on hip fracture incidence. Administrative billing data were used to follow two cohorts of women aged 65 and older after starting
therapy with either
risedronate (n = 86,735) or
raloxifene (n = 37,726). The fracture risk profile was described using a 6-month history period before starting
therapy. Effectiveness of each
therapy was evaluated by comparing the incidence of
hip fractures during the first 3 months with the subsequent 12 months among women adherent (medication possession ratio >80%) compared with those non-adherent to treatment. At the start of
therapy, the
raloxifene cohort was younger than the
risedronate cohort (median age 73 vs. 76 years) and had fewer prior fractures (p < 0.01 for both). In the first 3 months of
therapy, hip fracture incidence was lower in the
raloxifene group (0.51 per 100 person-years) compared with the
risedronate group (0.94 per 100 person-years). In the subsequent 12 months, the incidence of
hip fractures decreased among patients adherent to the
risedronate regimen [relative risk (RR) 0.70, 95% CI 0.59-0.84, p < 0.01] and did not change significantly among patients adherent to the
raloxifene regimen (RR 1.02, 95% CI 0.73-1.44). In poorly adherent patients, neither
drug decreased hip fracture risk.
Risedronate treatment in adherent patients rapidly decreased the risk of
hip fractures, whereas
raloxifene treatment did not.