OBJECTIVES: The objective of this early postlaunch analysis was to examine medication persistence among women °Ý45 years and newly prescribed monthly or weekly bisphosphonate (BP) therapy at 9 months. METHODS: The i3 Innovus administrative claims database was used to retrospectively identify female patients who filled a new prescription for a weekly BP (risedronate or alendronate) or monthly ibandronate starting in April 2005. Medication persistence was defined as having no refill gaps exceeding grace periods of 30 (weekly BPs) and 45 days (monthly BPs). Cox proportional hazard analysis was used to control for the effects of potential confounding factors including age, co-pay, and co-morbidities. RESULTS: This analysis included 967 women prescribed monthly ibandronate and 8662 women prescribed weekly BPs. At 9-months, the median number of days until discontinuation was 236 days for monthly and 141 days for weekly (p<0.0001). Significantly more patients receiving monthly ibandronate were persistent compared to patients receiving weekly BPs (48% vs 35%, P<0.0001). After adjusting for potential confounding factors, monthly users overall were 38.0% more likely to persist with therapy versus weekly users (hazard ratio=0.620, 95% CI 0.563-0.683, P<0.0001). CONCLUSION: The 9-month results of this analysis indicate that more women on monthly therapy are persistent than women on weekly bisphosphonates. This early finding suggests enhanced long-term persistence with ibandronate monthly therapy, with the potential for improved clinical outcomes. Follow-up of this cohort is ongoing.