SGLT2 inhibitors and metformin: Dual antihyperglycemic therapy and the risk of metabolic acidosis in type 2 diabetes

The prevalence of type 2 diabetes mellitus (T2D) has risen in the United States and worldwide, with an increase in global prevalence from 4.7% to 8.5% between 1980 and 2014. A variety of antidiabetic drugs are available with different mechanisms of action, and multiple drugs are often used concomitantly to improve glycemic control. One of the newest classes of oral antihyperglycemic agents is the sodium glucose cotransporter-2 (SGLT2) inhibitors or “flozins”. Recent clinical guidelines have suggested the use of SGLT2 inhibitors as add-on therapy in patients for whom metformin alone does not achieve glycemic targets, or as initial dual therapy with metformin in patients who present with higher glycated hemoglobin (HbA1c) levels. The FDA has approved fixed-dose combination (FDC) tablets with each of the three available SGLT2 inhibitors (canagliflozin, dapagliflozin, and empagliflozin) and metformin. Both drug classes are associated with the rare but serious life-threatening complications that result from metabolic acidosis, including lactic acidosis (with metformin) and euglycemic diabetic ketoacidosis (with SGLT2 inhibitors). This review summarizes the current literature on the pharmacokinetics and the molecular targets of metformin and SGLT2 inhibitors. It also addresses the common adverse effects and highlights the molecular mechanisms by which this dual antihyperglycemic therapy contributes to high anion gap metabolic acidosis. In conclusion, while the combination of metformin and SGLT2 inhibitors would be a better option in improving glycemic control with a low risk of hypoglycemia, an increase in the risk of metabolic acidosis during combination therapy may be borne in mind.