Background: Although patients with type 2 diabetes mellitus (T2DM) may fail to achieve adequate hemoglobin A1c (HbA1c) control despite metformin-sulfonylurea (Met-SU) dual therapy, a third-line glucose-lowering medication-including dipeptidyl peptidase-4 inhibitor (DPP4i), insulin, or thiazolidinedione (TZD)-can be added to achieve this. However, treatment effects of intensification with the medications on the risk of severe hypoglycemia (SH), cardiovascular disease (CVD), and all-cause mortality are uncertain. Study aim was to compare the risks of all-cause mortality, CVD, and SH among patients with T2DM on Met-SU dual therapy intensified with DPP4i, insulin, or TZD.
Methods and findings: We analyzed a retrospective cohort data of 17,293 patients with T2DM who were free from CVD and on Met-SU dual therapy and who were intensified with DPP4i (n = 8,248), insulin (n = 6,395), or TZD (n = 2,650) from 2006 to 2017. Propensity-score weighting was used to balance out baseline covariates across groups. Hazard ratios (HRs) for all-cause mortality, CVD, and SH were assessed using Cox proportional hazard models. Mean age of all patients was 58.56 ± 11.41 years. All baseline covariates achieved a balance across the 3 groups. Over a mean follow-up period of 34 months with 49,299 person-years, cumulative incidences of all-cause mortality, SH, and CVD were 0.061, 0.119, and 0.074, respectively. Patients intensified with insulin had higher risk of all-cause mortality (HR = 2.648, 95% confidence interval [CI] 2.367-2.963, p < 0.001; 2.352, 95% CI 2.123-2.605, p < 0.001) than those intensified with TZD and DPP4i, respectively. Insulin users had the greatest risk of SH (HR = 1.198, 95% CI 1.071-1.340, p = 0.002; 1.496, 95% CI 1.342-1.668, p < 0.001) compared with TZD and DPP4i users, respectively. Comparing between TZDs and DPP4i, TZDs were associated with a higher risk of SH (HR = 1.249, 95% CI 1.099-1.419, p < 0.001) but not all-cause mortality (HR = 0.888, 95% CI 0.776-1.016, p = 0.084) or CVD (HR = 1.005, 95% CI 0.915-1.104, p = 0.925). Limitations of this study included the lack of data regarding lifestyle, drug adherence, time-varying factors, patients' motivation, and cost considerations. A limited duration of patients intensifying with TZD might also weaken the strength of study results.
Conclusions: Our results indicated that, for patients with T2DM who are on Met-SU dual therapy, the addition of DPP4i was a preferred third-line medication among 3 options, with the lowest risks of mortality and SH and posing no increased risk for CVD events when compared to insulin and TZD. Intensification with insulin had the greatest risk of mortality and SH events.