[Traditional contraindications to the use of metformin -- more harmful than beneficial?].

For fear of lactic acidosis the currently listed contraindications to the use of metformin exclude a large number of people with type 2 diabetes from efficacious anti-hyperglycemic and cardioprotective treatment. Yet recent data call the traditional contraindications to metformin into question. As the incidence of lactic acidosis in patients with type 2 diabetes is the same with or without metformin therapy (about 9 per 100,000 patient years) there is no evidence that metformin therapy is associated with an increased risk of lactic acidosis. Similarly, despite disregard internationally of major metformin contraindications, there has been no corresponding increase in the incidence of lactic acidosis. Metformin treatment of elderly diabetics with multiple comorbidities and explicit contraindications has led to significantly better clinical parameters in them than in the control group without metformin; and there were no cases of lactic acidosis. The two groups did not differ with regard to progression of renal failure, patient-oriented endpoints or overall mortality. Compared with its predecessors phenformin and buformin, metformin is considerably less lipophilic and has a shorter plasma half-life; it is eliminated renally in unchanged form. In type 2 diabetics treated with metformin -- even those over 70 years of age and those in mild renal failure -- no relevant increases in lactate levels were found. In patients with lactic acidosis there was no correlation between the levels of metformin and lactate. The prognosis of lactic acidosis is determined less by the serum concentrations of metformin and lactate than by the hypoxia caused by the underlying disease and comorbidities. These findings raise doubts about the significance of metformin in the pathogenesis of lactic acidosis. On the basis of the current data, advanced age per se, mild renal impairment and stable heart failure can no longer be upheld as contraindications to the use of metformin. It should be safe to withdraw metformin the evening before radiological examinations with intravenous contrast media or surgical procedures under general anaesthesia in diabetics with normal renal function.