Metformin lactic acidosis: Should we still be afraid?

Metformin, the first choice drug for type 2 diabetes treatment in all stages of therapy, and one of the most widely prescribed anti-hyperglycemic agents worldwide, represents a rare example of an old drug which continues to display new beneficial effects in various fields. However, lactic acidosis (LA) persists as a serious adverse effect. LA incidence is low and is not necessarily determined by the administration of metformin. Unfortunately, the concern for this complication has negatively affected the drug use, particularly in chronic kidney disease, which may impair drug excretion, and in congestive heart failure and chronic liver disease, which may promote lactate accumulation. This review describes how not only these historical contraindications have been considerably scaled back, though rather a recent large body of evidence supports a protective effect of biguanide on kidney, heart and liver and, maybe, against lactic acidosis itself. It is worthy to slow down both contraindications and precautions to metformin use, not to deprive a significant number of diabetic patients, as those with kidney, heart and liver comorbidities, from its potential benefits, and not to hamper in the near future the putative advantages in a wide spectrum of conditions outside of diabetes.