Gastrointestinal events and association with initiation of treatment for osteoporosis Ankita Modi,1 Ethel S Siris,2 Jackson Tang,3 Shiva Sajjan,1 Shuvayu S Sen1 1Center for Observational and Real-World Evidence, Merck & Co., Inc, Kenilworth, NJ, 2Toni Stabile Osteoporosis Center, Columbia University Medical Center, NY Presbyterian Hospital, New York, NY, 3Asclepius Analytics Ltd, Brooklyn, NY, USA Background: Preexisting gastrointestinal (GI) events may deter the use of pharmacologic treatment in patients diagnosed with osteoporosis (OP). The objective of this study was to examine the association between preexisting GI events and OP pharmacotherapy initiation among women diagnosed with OP. Methods: The study utilized claims data from a large US managed care database to identify women aged ≥55 years with a diagnosis code for OP (index date) during 2002–2009. Patients with a claim for pharmacologic OP treatment in the 12-month pre-index period (baseline) were excluded. OP treatment initiation in the post-index period was defined as a claim for bisphosphonates (alendronate, ibandronate, risedronate, zoledronic acid), calcitonin, raloxifene, or teriparatide. During the post-index period (up to 12 months), GI events were identified before treatment initiation. A time-dependent Cox regression model was used to investigate the likelihood of initiating any OP treatment. Among patients initiating OP treatment, a discrete choice model was utilized to assess the relationship between post-index GI events and likelihood of initiating with a bisphosphonate versus a non-bisphosphonate. Results: In total, 65,344 patients (mean age 66 years) were included; 23.7% had a GI event post diagnosis and before treatment initiation. Post-index GI events were associated with a 75% lower likelihood of any treatment initiation (hazard ratio 0.25; 95% confidence interval 0.24–0.26). Among treated patients