Measurements of medication adherence in diabetic patients with poorly controlled HbA(1c).

AIMS

To assess pharmacy claims and self-report data as measures of medication adherence and to describe baseline characteristics of subjects in the Improving Diabetes Outcomes Study.

METHODS

Multi-ethnic, lower-income, insured adults (n = 526) in New York City with Type 2 diabetes were enrolled in a randomized, controlled, behavioural intervention study delivered by telephone. Baseline data were examined, including glycated haemoglobin (HbA(1c)), objective measures of diabetes medication adherence [claims data medication possession ratio (MPR)], and two self-report measures [Morisky Medication-taking Scale and the medication-taking item of the Summary of Diabetes Self-Care Activities (SDSCA)]. Associations of highest tertile HbA(1c) (>or= 9.3%) with lowest tertile MPR (< 42%) were assessed with logistic regression models adjusting for potential confounders. Subset analyses were performed based on assessment of potential interaction.

RESULTS

Participants (mean +/- sd age 56 +/- 7 years) had median (interquartile range) HbA(1c) 8.6% (8.0-10.0). Correlations of baseline MPR with Morisky score and SDSCA medication-taking item were strongly significant (both rho = 0.21, P < 0.001). Lowest MPR was significantly (P = 0.008) associated with highest HbA(1c) in the group as a whole and among the subset taking two or more oral glucose-lowering agents (OGLA) (P = 0.002), but not among the subset taking only one (P = 0.83). Self-report adherence measures were not significantly associated with HbA(1c) in either the whole group or either subset.

CONCLUSIONS

These results support the validity of MPR as an adherence measure for OGLA among insured diabetes patients with poorly controlled HbA(1c), especially those taking two or more OGLA.