Adherence to prescribed oral hypoglycaemic medication in a population of patients with Type 2 diabetes: a retrospective cohort study

Aims To evaluate the patterns and predictors of adherence in all patients with Type 2 diabetes in the community receiving treatment with a single oral hypo glycaemic drug. In particular, to test the hypothesis that one tablet per day is associated with better adherence than more than one. Methods The study design was a retrospective cohort study set in the Tayside region of Scotland (population approx. 400 000). Participants were residents of Tayside from 1 January 1993 until 31 December 1995 with at least 12 months of prescriptions of oral hypoglycaemic drugs (OHDs). The main outcome measures were adherence indices for sulphonylureas and metformin separately, adjusting for prescribing while hospitalized. Results Of the total 2920 subjects identified, adequate adherence (greater than or equal to 90%) was found in 31 % of those prescribed sulphonylureas alone (n = 1329, median adherence = 300 days per year), and in 34 % of those prescribed metformin alone (n = 528, median = 302 days per year). There were significant linear trends of poorer adherence with each increase in the daily number of tablets taken (p = 0.001) and increase in co-medication (p = 0.0001) for sulphonylureas alone after adjustment for other factors. Conclusions In the community only one in three with Type 2 diabetes had adequate adherence to OHDs. One tablet per day administration was associated with greater adherence than multiple tablets. Poor adherence is a major obstacle to the benefit of complex drug regimens in the treatment of Type 2 diabetes.