Objective: To report 2 cases of lactic acidemia associated with the use of metformin in patients with normal renal function.
Case summary: An 82-year-old African American man and a 76-year-old white man developed an elevated serum lactic acid concentration a few weeks after initiation of metformin therapy for type 2 diabetes. After the patients discontinued metformin, the serum lactic acid concentration normalized in both cases. An objective causality assessment revealed that the adverse drug event was probably related to the use of metformin.
Discussion: Metformin interferes with the production and elimination of lactic acid by a variety of mechanisms that are not well understood. Few systematic data are available on changes in plasma lactic acid concentrations in patients with type 2 diabetes and normal renal function. Clinical significance of a high serum lactic acid concentration needs clarification.
Conclusions: Metformin therapy can be associated with subclinical elevation of lactic acid concentration in the absence of renal insufficiency or other contraindications to using this agent in patients with type 2 diabetes. Periodic monitoring of basic metabolic panels may prevent this potentially serious complication of metformin therapy.