Adherence with intravenous zoledronate and intravenous ibandronate in the United States Medicare population.
OBJECTIVE
To evaluate adherence to drug therapy among new users of zoledronate and intravenous (IV) ibandronate among US Medicare enrollees.


METHODS
We used data from the Medicare 5% random sample to evaluate new users of IV zoledronate and IV ibandronate with continuous Part A and Part B fee-for-service coverage. The outcome was adherence as quantified by the proportion of days covered (PDC) measured continuously and dichotomously (≥ 80%). Followup time extended from 18-27 months for all individuals. Factors associated with low adherence to zoledronate were evaluated with logistic regression.


RESULTS
We identified 775 new users of zoledronate and 846 new users of IV ibandronate. For both drugs, 30-48% of the first infusions were given in an outpatient infusion center, not in a physician's office. The mean PDC for zoledronate users was 82%, which was greater than the mean PDC for the IV ibandronate users (58-62% depending on the time period; P < 0.0001). Approximately 30% of zoledronate users did not receive a second infusion. Factors associated with low adherence to zoledronate included older age and receipt of the first infusion in an outpatient infusion center rather than a physician's office.


CONCLUSIONS
Less frequently dosed IV bisphosphonates have not resolved the problem of suboptimal adherence with prescription osteoporosis medications. Interventions continue to be warranted to improve long-term adherence to osteoporosis treatments.
University of Alabama at Birmingham, AL, USA. jcurtis@uab.edu
Jeffrey R
JR
Curtis
Huifeng
H
Yun
Robert
R
Matthews
Kenneth G
KG
Saag
Elizabeth
E
Delzell
D000368:Aged; D000369:Aged, 80 and over; D050071:Bone Density Conservation Agents / Q000008:administration & dosage / Q000627:therapeutic use; D004164:Diphosphonates / Q000008:administration & dosage* / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D000077557:Ibandronic Acid; D007093:Imidazoles / Q000008:administration & dosage* / Q000627:therapeutic use*; D007262:Infusions, Intravenous; D016015:Logistic Models; D008297:Male; D006278:Medicare; D010024:Osteoporosis / Q000188:drug therapy*; D010349:Patient Compliance; D014481:United States; D000077211:Zoledronic Acid; D016903:Drug Monitoring
D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D007093:Imidazoles; D000077211:Zoledronic Acid; D000077557:Ibandronic Acid