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.