Second-line Glucose-Lowering Therapy in Type 2 Diabetes Mellitus

There is consensus that metformin should be the first-line pharmacological therapy for type 2 diabetes. Although new evidence on effective treatments for type 2 diabetes is rapidly evolving, there is uncertainty regarding the optimal choice of second-line therapy. Our aim was to review the current major guidelines for second-line therapy in type 2 diabetes, along with findings from the recent cardiovascular outcome trials, focusing on two particularly promising classes of glucose-lowering drugs, sodium-glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide 1 receptor agonists (GLP1 RAs).

In the recent randomized controlled trials, two SGLT2 inhibitors (i.e., empagliflozin and canagliflozin) and two GLP1 RAs (i.e., liraglutide and albiglutide) reduced cardiovascular events in patients with type 2 diabetes, of whom most had established atherosclerotic cardiovascular disease. Some clinical guidelines have changed their recommendations for second-line therapy based on these findings. The first choice for a second-line therapy by the new American Diabetes Association/European Association for the Study of Diabetes (ADA/EASD) guidelines is SGLT2 inhibitors or GLP1 RAs for patients with atherosclerotic cardiovascular disease, heart failure, or chronic kidney disease. For patients without these conditions, the ADA/EASD lists five options of noninsulin second-line therapy without a suggested hierarchy of use. On the other hand, the 2019 consensus statement from the American Association of Clinical Endocrinologists/American College of Endocrinology lists nine hierarchical options, with GLP1 RAs as the first recommended therapy, followed by SGLT2 inhibitors and dipeptidyl peptidase 4 (DPP4) inhibitors, and sulfonylurea as the last option. The American College of Physicians recommends four oral treatment options, which do not include GLP1 RAs. The International Diabetes Federation recommends sulfonylureas, DPP4 inhibitors, or SGLT2 inhibitors as preferred second-line drugs with GLP1 RAs as an alternative in obese patients. The World Health Organization strongly recommends sulfonylureas in low-resource settings. The National Institute for Health and Care Excellence in the UK recommends DPP4 inhibitors, thiazolidinediones, or sulfonylureas, with use of SGLT2 inhibitors only under special circumstances.

Clinical guidelines for the choice of second-line therapy in type 2 diabetes are inconsistent. A comprehensive assessment of the risks and benefits of second-line therapy is needed to address knowledge gaps that underlie core clinical practice.