Cardiovascular risks associated with second-line oral antidiabetic agents added to metformin in patients with Type 2 diabetes: a nationwide cohort study

Aim To compare the cardiovascular risks associated with second-line oral antidiabetic agents added to initial metformin therapy in a large nationwide observational study. Methods We conducted a nationwide retrospective cohort study using the Taiwan National Health Insurance database. A total of 36 118 users of different add-on oral antidiabetic agents (sulphonylureas, glinides, pioglitazone, α-glucosidase inhibitors and dipeptidyl peptidase-4 inhibitors) after initial metformin therapy were included in the analysis. The reference group was sulphonylureas added to metformin, the most commonly used combination regimen. The main outcomes of interest were hospitalizations for any cardiovascular event including acute myocardial infarction, congestive heart failure and ischaemic stroke. In the main analysis, all patients were followed within their initiation groups until the study end, disregarding any changes in treatment status over time. Results In intention-to-treat analyses, there was no difference in the risk of any cardiovascular event among the add-on combination treatment groups, but significantly lower risks of acute myocardial infarction were found for the glinides plus metformin treatment group (crude hazard ratio 0.52, adjusted hazard ratio 0.39; 95% CI 0.20–0.75) and for the α-glucosidase inhibitors plus metformin treatment group (crude hazard ratio 0.63, adjusted hazard ratio 0.54; 95% CI 0.31–0.95). No difference in risk of congestive heart failure or ischaemic stroke risk was found among the combination treatment groups. In secondary as-treated analyses, similar but less significant associations were found as compared with the primary intention-to-treat analyses for all treatment groups. Conclusion There were no differences in overall cardiovascular risks among several add-on second-line oral antidiabetic agents; however, glinide plus metformin and α-glucosidase inhibitors plus metformin combination therapies might be associated with lower risks of acute myocardial infarction.