Persistence with weekly and monthly bisphosphonates among postmenopausal women: analysis of a US pharmacy claims administrative database

Background: Bisphosphonates are available in daily, weekly, and monthly dosing formulations to treat postmenopausal osteoporosis. Some researchers suggested that adherence to monthly bisphosphonate might be different from that with weekly or daily bisphosphonate because of different dosing regimens. However, the actual persistency rates in regular practice settings are unknown. Objectives: To compare persistence rates with alendronate 70 mg once weekly (AOW), risedronate 35 mg once weekly (ROW), and ibandronate 150 mg once monthly (IOM) in a US pharmacy claims database. Methods: In this retrospective cohort study, pharmacy claims data of patients with new bisphosphonate prescriptions were extracted for women aged >= 50 years who had an AOW, ROW, or IOM prescription (index prescription) between December 30, 2004 and May 31, 2005 (the index period) and did not have the index Rx during the previous 12 months. Patients' records were reviewed for at least 5 months from their index date to November 2, 2005 (the follow-up period). Patients were considered persistent if they neither discontinued (failed to refill the index Rx within a 45-day period following the last supply day of the previous dispensing) nor switched (changed to another bisphosphonate) during the follow-up period. Medication-possession ratio was defined as days with index prescription supplies/total days of follow-up. Results: Among 44,635 patients, 25,207 (56.5%) received prescriptions of AOW, 18,689 (41.9%) ROW, and 739 (1.7%) IOM as the index prescription. In all, 35.1% of AOW patients, 32.5% of ROW patients, and 30.4% of IOM patients (P < 0.0001 AOW vs ROW or IOM) had persisted with their initial therapy, whereas 64.0% of AOW, 66.4% of ROW, and 68.2% of IOM patients discontinued (P < 0.0001) during follow-up. The medication-possession ratio (days with index prescription supplies/total days of follow-up) was significantly higher for AOW (0.55) compared with ROW (0.52) and IOM (0.51, P < 0.05). By Kaplan-Meier analysis, the time for 50% of patients to discontinue therapy was also significantly longer with AOW (109 days) compared with ROW (95 days, P < 0.05) or IOM (58 days, P < 0.05). Conclusion: In a real-world clinical setting, although persistence with all treatments was suboptimal, patients receiving prescriptions for once-weekly alendronate were more likely to be persistent than those receiving prescriptions for once-weekly risedronate or once-monthly ibandronate.