Evolving channeling in prescribing SGLT-2 inhibitors as first-line treatment for type 2 diabetes

Purpose Sodium-glucose cotransporter-2 inhibitors (SGLT-2i) are increasingly being considered as first-line treatment for type 2 diabetes (T2D). The benefits of SGLT-2i from cardiovascular outcome trials may lead to preferential prescribing of SGLT-2i to patients at high cardiovascular risk, possibly causing confounding in non-randomized studies of SGLT-2i as first-line treatment. We assessed evolving imbalances in characteristics of patients starting SGLT-2i versus metformin as first-line monotherapy. Methods Using claims data from two US commercial health insurance and Medicare, we identified patients with T2D aged >= 18 years (>65 years in Medicare) initiating first-line SGLT-2i or metformin from 2013 through 2019. Standardized differences (SDs) for patient characteristics were assessed during four consecutive calendar time blocks (T1:4/2013-12/2014; T2:1/2015-6/2016; T3:7/2016-12/2017; and T4:1/2018-12/2019). We also estimated the propensity score of receiving SGLT-2i versus metformin within each time block and evaluated time trends in model discrimination with c-statistics. Results We identified 9113 initiators of first-line SGLT-2i and 810 348 initiators of first-line metformin. During T1, SGLT-2i initiators were younger (SD = -0.24) and less likely to have seen cardiologists (-0.07) with a similar prevalence of CVD (0.04) compared with metformin. During T4, patients were more balanced for age (-0.01). Cardiologist visits (0.08) and CVD (0.25) became more prevalent among SGLT-2i initiators. Conclusions When comparing initiators of first-line SGLT-2i versus metformin, imbalances in patient characteristics evolved from 2013 through 2019, particularly channeling SGLT-2i to individuals at high cardiovascular risk. Evolving channeling in prescribing first-line SGLT-2i should be expected and accounted for in non-randomized comparative effectiveness research.