Adherence and occurrence of fractures after switching to once-monthly oral bisphophonates.
OBJECTIVE
Reducing dosing demands of medications generally increases adherence, although this relationship has not been demonstrated with the once-monthly oral bisphosphonates (BP). The study aim is to test whether switching from once-weekly BPs to once-monthly BPs improves adherence and fracture risk.


METHODS
This is an interrupted times-series analysis of new users of once-weekly BPs in a nationwide administrative health database from 2003 to 2007. Participants include 1835 individuals who switched to once-monthly BPs and two propensity-matched comparator groups: 1835 individuals who switched to a different once-weekly BP, and 1835 who did not switch. We measured changes in adequate adherence pre- and post-switch as monthly medication possession ratio >0.80, and calculated incidence rate ratios (IRR) of osteoporotic fractures.


RESULTS
All study groups experienced major adherence failure in the first year of therapy: the proportion of adequate adherers was 42% among once-monthly switchers, 47% among once-weekly switchers, and 37% among nonswitchers. However, the once-monthly switch was associated with less adherence failure (4% fewer adherers per month pre-switch vs. 1% fewer adherers per month post-switch, p<0.000). There was no statistically significant change in adherence rates for the other groups. We did not detect significantly reduced fracture risk with once-monthly switch: 1 year post-switch, the fracture incidence risk ratios for once-monthly switchers relative to once-weekly switchers were IRR 0.83, 95% CI: 0.50-1.36, and IRR 0.90, 95% CI: 0.54-1.49, relative to nonswitchers).


CONCLUSIONS
Reducing the dosing demands of oral bisphosphonates from once-weekly to once-monthly decreased adherence failure but had an uncertain impact on fracture risk.
Meyers Primary Care Institute, Fallon Clinic and the Fallon Community Health Plan Worcester, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA. Becky.Briesacher@umassmed.edu
Becky A
BA
Briesacher
Susan E
SE
Andrade
Leslie R
LR
Harrold
Hassan
H
Fouayzi
Robert A
RA
Yood
D050071:Bone Density Conservation Agents / Q000008:administration & dosage*; D016208:Databases, Factual; D004164:Diphosphonates / Q000008:administration & dosage*; D004334:Drug Administration Schedule; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D006801:Humans; D008297:Male; D055118:Medication Adherence; D008875:Middle Aged; D010024:Osteoporosis / Q000150:complications / Q000188:drug therapy
D050071:Bone Density Conservation Agents; D004164:Diphosphonates