Mortality and Other Important Diabetes-Related Outcomes With Insulin vs Other Antihyperglycemic Therapies in Type 2 Diabetes

CONTEXT: The safety of insulin in the treatment of type 2 diabetes mellitus (T2DM) has recently undergone scrutiny. OBJECTIVE: The objective of the study was to characterize the risk of adverse events associated with glucose-lowering therapies in people with T2DM. DESIGN AND SETTING: This was a retrospective cohort study using data from the UK General Practice Research Database, 2000–2010. PATIENTS: Patients comprised 84 622 primary care patients with T2DM treated with one of five glucose-lowering regimens: metformin monotherapy, sulfonylurea monotherapy, insulin monotherapy, metformin plus sulfonylurea combination therapy, and insulin plus metformin combination therapy. There were 105 123 exposure periods. MAIN OUTCOME MEASURES: The risk of the first major adverse cardiac event, first cancer, or mortality was measured. Secondary outcomes included these individual constituents and microvascular complications. RESULTS: In the same model, and using metformin monotherapy as the referent, the adjusted hazard ratio (aHR) for the primary end point was significantly increased for sulfonylurea monotherapy (1.436, 95% confidence interval [CI] 1.354–1.523), insulin monotherapy (1.808, 95% CI 1.630–2.005), and insulin plus metformin (1.309, 95% CI 1.150–1.491). In glycosylated hemoglobin/morbidity subgroups, patients treated with insulin monotherapy had aHRs for the primary outcome ranging from 1.469 (95% CI 0.978–2.206) to 2.644 (95% CI 1.896–3.687). For all secondary outcomes, insulin monotherapy had increased aHRs: myocardial infarction (1.954, 95% CI 1.479–2.583), major adverse cardiac events (1.736, 95% CI 1.441–2.092), stroke (1.432, 95% CI 1.159–1.771), renal complications (3.504, 95% CI 2.718–4.518), neuropathy (2.146, 95% CI 1.832–2.514), eye complications (1.171, 95% CI 1.057–1.298), cancer (1.437, 95% CI 1.234–1.674), or all-cause mortality (2.197, 95% CI 1.983–2.434). When compared directly, aHRs were higher for insulin monotherapy vs all other regimens for the primary end point and all-cause mortality. CONCLUSIONS: In people with T2DM, exogenous insulin therapy was associated with an increased risk of diabetes-related complications, cancer, and all-cause mortality. Differences in baseline characteristics between treatment groups should be considered when interpreting these results.