Comparison of the effects of once-monthly versus once-daily risedronate in postmenopausal osteoporosis: a phase II, 6-month, multicenter, randomized, double-blind, active-controlled, dose-ranging study.

BACKGROUND: Risedronate 5 mg/d is approved by the US Food and Drug Administration for the treatment and prevention of postmenopausal osteoporosis. Once-monthly dosing options might increase treatment compliance and persistence.

OBJECTIVE: The aim of this study was to compare the tolerability and efficacy of 3 once-monthly risedronate dosing regimens with those of risedronate 5 mg/d.

METHODS: This Phase II, 6-month, randomized, double-blind, active-controlled, dose-ranging study was conducted at 13 clinical research centers and hospitals in Croatia, Poland, Canada, and the United States between April 2004 and June 2005. Post-menopausal women aged 50 to 85 years with a lumbar spine T-score <-2.0 were randomly assigned to 1 of 4 treatment groups: risedronate 100, 150, or 200 mg/mo or 5 mg/d (active control), administered PO for 6 months. Evaluation of tolerability, the primary study objective, was based on adverse-event (AE) profiles and clinical laboratory values. Efficacy evaluation, a secondary objective, was a noninferiority comparison of the changes from baseline in bone mineral density (BMD) and bone turnover markers (BTMs).

RESULTS: Of 370 patients randomized (91, 88, 88, and 103 patients in the risedronate 100-, 150-, and 200-mg/mo and 5-mg/d groups, respectively), 57% were > or =65 years of age and 99% were white; 316 patients (85.4%) completed the study. Completion rates were not significantly different across treatment groups, nor were reasons for discontinuation. Between-group differences in the incidences of treatment-emergent AEs, serious AEs, and upper gastrointestinal (GI) AEs were nonsignificant. Overall, 6 (7%), 14 (16%), 6 (7%), and 9 patients (9%) withdrew because of AEs in the 100-, 150-, and 200-mg/mo and 5 mg/d groups, respectively. GI disorders were the AEs that most frequently led to study withdrawal (5 [5.5%], 7 [8.0%], 4 [4.5%], and 6 [5.8%]). No trends were observed in the nature or frequency of other AEs causing withdrawal. All serious AEs were considered unrelated to treatment, with the exception of erosive esophagitis in 1 patient (1%) who received the 5-mg/d dose. Mean percentage increases in BMD were 2.10%, 2.99%, and 3.38% with risedronate 100, 150, and 200 mg/mo, respectively, versus 3.05% with 5 mg/d. At the 2 higher monthly doses, the changes from baseline in BMD were not significantly different from those in the 5-mg/d group. Mean BTM values were decreased significantly from baseline in all 4 treatment groups, and the changes from baseline at 6 months at the 2 higher monthly doses were not significantly different from those at 5 mg/d.

CONCLUSIONS: Overall, in this study, the safety profiles of risedronate 100, 150, and 200 mg/mo were not different from that of risedronate 5 mg/d. Changes in efficacy measures in the monthly treatment groups were considered dose related and were not significantly different between the 5-mg/d group and the 150- and 200-mg/mo groups; similarity was greatest with 150 mg/mo.