Clinical backgrounds associated with discrepancy between subjective and objective assessments of medication adherence in Japanese type 2 diabetic patients

Although medication adherence can be easily assessed by self-reports in clinical practice, accuracy is sometimes questionable. To make full use of self-reports on medication adherence in clinical practice, understanding the discrepancy between subjectively and objectively assessed adherence is important. The aim of this study was to investigate which clinical characteristics would be associated with such discrepancy regarding adherence to oral antidiabetic drugs (OADs) in type 2 diabetic patients. Our study assessed 406 Japanese type 2 diabetic outpatients treated with OADs. Medication adherence to OADs was evaluated in percentage, both subjectively by self-report and objectively by pill counts on the same day. We developed a common regression model by extending the generalized linear mixed model and statistically detected the difference in the impact of clinical characteristics between the two measures. Subjectively measured adherence was higher than objectively measured adherence, showing a 1.6-fold difference in odds (p < 0.001). Male gender, older age, longer diabetic duration, and taking more than two OADs daily were independently associated with the overrating of medication adherence by self-report compared with the objectively measured adherence. On the other hand, higher glycocylated hemoglobin (HbA1c) levels, taking medication before meals, and taking medication outside the home were independently associated with underrating medication adherence by self-report. In conclusion, this study demonstrated clinical characteristics associated with overrating and underrating of medication adherence by self-report in Japanese type 2 diabetic patients treated with OADs.