title: Medication adherence and fracture risk among patients on bisphosphonate therapy in a large United States health plan.
abstract: The association between bisphosphonate adherence in the first 12 months after therapy initiation and subsequent fracture risk was examined. Patients were identified from a large, commercially-insured population with integrated pharmacy and medical claims. Eligible patients were aged ≥45 years, were new to osteoporosis therapy (no osteoporosis medication claims in prior year) with first (index) bisphosphonate claim between 1/1/2005 and 4/30/2008, and had continuous insurance coverage for ≥12 months pre- and post-index. Patients with fracture claims ≤12-months post-index were excluded. Adherence was assessed using the medication possession ratio (MPR) over 12-months post-index (i.e., sum of days' supply dispensed divided by 365 days). Patients with a MPR>0.8 were considered adherent. The follow-up period to assess incident fracture began at month 13. The analysis included 33,558 new bisphosphonate users with mean age (SD) 59.5 (9.3) years; 94.0% were female. Median MPR at 12 months was 0.61 for alendronate and risedronate; 0.58 for ibandronate. Proportionally more nonfracture patients (39.3%) had a MPR>0.8 compared with fracture patients (34.9%, p<0.001). In multivariate modeling of bisphosphonate users' experience, those with a MPR>0.8 had a 14% lower risk of subsequent fracture than those with MPR<0.5, after controlling for demographics, insurance type, select comorbidities, and other potential confounders (p=0.0459). In a large, commercially-insured population, suboptimal adherence with bisphosphonate treatment was associated with increased fracture risk even after controlling for potential confounders.
authors.affiliation: Wade Outcomes Research and Consulting, 358 South 700 East, Suite B 432, Salt Lake City, UT 84102, USA. sallyw@amgen.com
authors.forename: Sally W
authors.initials: SW
authors.lastname: Wade
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Curtis
authors.forename: Jingbo
authors.initials: J
authors.lastname: Yu
authors.forename: Jeffrey
authors.initials: J
authors.lastname: White
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Stolshek
authors.forename: Claire
authors.initials: C
authors.lastname: Merinar
authors.forename: Akhila
authors.initials: A
authors.lastname: Balasubramanian
authors.forename: Joel D
authors.initials: JD
authors.lastname: Kallich
authors.forename: John L
authors.initials: JL
authors.lastname: Adams
authors.forename: Hema N
authors.initials: HN
authors.lastname: Viswanathan
mesh_terms: D000368:Aged; D003710:Demography; D004164:Diphosphonates / Q000627:therapeutic use*; D005260:Female; D050723:Fractures, Bone / Q000188:drug therapy* / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013221:State Health Plans / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology; D016903:Drug Monitoring
chemical_list: D004164:Diphosphonates