Persistence across weekly and monthly bisphosphonates: analysis of US retail pharmacy prescription refills

Determine whether monthly dosing of bisphosphonates has an impact on persistence relative to weekly dosing.

We used the IMS Longitudinal Prescription database of retail prescription records to study 165,955 women aged 50 years or older newly initiated on therapy between September and November 2005 with no bisphosphonate prescriptions in the prior 12 months. All patients were followed for 365 days from their initial prescription and were considered persistent until they had a refill gap greater than 30 days between the end of the day's supply of one prescription and the beginning of the next. Proportional-hazards regression models were executed to compare persistence across bisphosphonates. Persistence may be underestimated because of the following: (1) we had no information on the receipt of samples; (2) we had no information about refills at pharmacies that did not participate in the IMS prescription database, (3) switched patients were excluded; and (4) the cohort was limited to patients newly initiated on bisphosphonates.

Patients initiating on monthly ibandronate had a lower average persistence duration (98 days) than weekly alendronate (116 days) and risedronate (113 days) patients (p < 0.0001). Based on the proportional-hazards model, monthly ibandronate patients were 10% more likely to discontinue than alendronate patients (HR = 1.10, p < 0.0001). After removing the patients who failed to refill after their initial prescription, persistence beyond patients' first refill were similar across the three bisphosphonates.

Monthly dosing does not appear to be associated with improvements in patient persistence with oral bisphosphonates for patients newly initiated on bisphosphonates.