The authors declare that they have no conflict of interest regarding this work.
Comparison of various measures for assessing medication refill adherence using prescription data†
Article first published online: 24 DEC 2008
Copyright © 2008 John Wiley & Sons, Ltd.
Pharmacoepidemiology and Drug Safety
Volume 18, Issue 2, pages 159–165, February 2009
How to Cite
Vink, N. M., Klungel, O. H., Stolk, R. P. and Denig, P. (2009), Comparison of various measures for assessing medication refill adherence using prescription data. Pharmacoepidem. Drug Safe., 18: 159–165. doi: 10.1002/pds.1698
- Issue published online: 22 JAN 2009
- Article first published online: 24 DEC 2008
- Manuscript Accepted: 12 NOV 2008
- Manuscript Revised: 4 NOV 2008
- Manuscript Received: 24 APR 2008
- patient compliance;
- diabetes mellitus type 2;
- administrative data;
- primary health care;
- drug utilization
Several measures using prescription data have been developed for estimating medication refill adherence. Few studies have made direct comparisons, and little is known about the accuracy of these measures in patients on a multiple-drug regimen.
To compare different calculation methods using prescription data for assessing refill adherence.
An observational cohort study among type 2 diabetes patients was conducted. Adherence to oral glucose-lowering, antihypertensive and lipid-lowering medication was assessed for 2004. We calculated medication possession ratios in a flexible period (MPRF), per calendar year (MPRY) and gaps between refills (GAP) at drug class and therapeutic level. Individual review of drug prescription profiles was conducted to validate identified cases of suboptimal refill adherence. Differences in Area Under the Curve (AUC) of ROC-curves were calculated to compare the methods.
Of the 3877 patients, 2969 (77%) patients received oral glucose-lowering medication, 2715 (70%) antihypertensives and 1797 (46%) lipid-lowering medication. Using cutoffs for MPR < 80% and GAP > 30 days, overall rates of suboptimal adherence for these drug classes were 32, 35 and 23% respectively. AUC for measures calculated at drug class level (range 0.85–0.90) were significantly larger than those calculated at therapeutic level (0.72–0.90). For oral glucose-regulating medication and antihypertensives, AUCs were largest for the MPRY and GAP measures (0.87–0.88). For lipid-lowering medication, the AUC was largest for the GAP measure (0.90).
Differences between adherence measures were small and favoured calculation on drug class level. For multiple drug use, both MPRY and GAP were good measures for identifying suboptimal refill adherence. Copyright © 2008 John Wiley & Sons, Ltd.