Real-world factors affecting adherence to insulin therapy in patients with Type 1 or Type 2 diabetes mellitus: a systematic review

Aims To identify real-world factors affecting adherence to insulin therapy in patients with Type1 or Type2 diabetes mellitus. Methods A literature search was conducted in PubMed and EMBASE in November 2011 to identify studies reporting factors associated with adherence/non-adherence to insulin therapy in adults with Type1 or Type2 diabetes. Results Seventeen studies were identified; six used self-reported measures and 11 used calculated measures of adherence. Most (13/17) were conducted exclusively in the USA. Four categories of factors associated with non-adherence were identified: predictive factors for non-adherence, patient-perceived barriers to adherence, type of delivery device and cost of medication. For predictive factors and patient-perceived barriers, only age, female sex and travelling were associated with non-adherence in more than one study. Fear of injections and embarrassment of injecting in public were also cited as reasons for non-adherence. Conversely, adherence was improved by initiating therapy with, or switching to, a pen device (in four studies), and by changing to an insurance scheme that lowered the financial burden on patients (in two studies). Conclusions Adherence to insulin therapy is generally poor. Few factors or patient-perceived barriers were consistently identified as predictive for non-adherence, although findings collectively suggest that a more flexible regimen may improve adherence. Switching to a pen device and reducing patient co-payments appear to improve adherence. Further real-world studies are warranted, especially in countries other than the USA, to identify factors associated with non-adherence and enable development of strategies to improve adherence to insulin therapy.