Lactic acidosis and metformin: warning about this avoidable risk

The National Medicines Safety Agency (ANSM) warns of the risks of lactic acidosis with metformin, in particular in patients with impaired kidney function, cardiorespiratory disease or sepsis (serious infection).

A known side effect of metformin

Lactic acidosis is a known side effect of metformin (list of medicines containing metformin). It can lead to death if treated too late. Certain situations are likely to promote its appearance and the signs that should lead to urgent medical attention.

Metformin is indicated for the treatment of type 2 diabetes. It is eliminated by the kidney. The risk of lactic acidosis increases when renal function declines. This risk of serious adverse effects can be limited by the following measures:

• Monitoring of the patient’s renal function and prescription of a dosage of metformin adapted to the renal function;
• Evaluation of the risk of worsening renal function by taking into account nephrotoxic drugs and/or possible dehydration which may increase the risk of lactic acidosis;
• Discontinuation of metformin and increased monitoring of renal function in the event of injection of iodinated contrast products, ensuring correct hydration during their use;
• Transitory discontinuation of metformin for acute dehydration (diarrhoea, severe vomiting, fever, or decreased fluid intake) with resumption once dehydration is corrected and in the absence of worsening renal function;
• Vigilance in the event of unbalanced diabetes and/or occurrence of acute conditions likely to alter renal function and/or decompensation of a chronic disease (recent myocardial infarction, acute heart failure, respiratory failure, shock, etc.) which are situations at risk of lactic acidosis.

Advice for patients to prevent these complications

For patients on metformin, the ANSM provides key information:

• Strictly follow the dosage prescribed by your doctor;
• Tell your doctor what treatments you are taking, especially if they are medicines for high blood pressure, heart failure, pain and inflammation (nonsteroidal anti-inflammatory drugs, or NSAIDs) or medicines that increase the production of urine (diuretics). Your doctor will assess whether these treatments are compatible with taking metformin;
• Ask your doctor or pharmacist for advice if you need to perform a radiological examination with injection of a contrast product containing iodine;
• Avoid excessive alcohol consumption, as well as prolonged fasting;
• Drink water regularly (1.5 to 2 liters per day): sufficient hydration with control of kidney function often helps to avoid the risk of lactic acidosis;
• Be vigilant in case of dehydration, this can occur as a result of vomiting, diarrhea, fever, exposure to heat, or only by drinking less water than usual;
• Tell your doctor in the following situations that are more at risk of causing lactic acidosis: diarrhea, poorly controlled diabetes, serious infections, liver problems or heart disease, rapid weight loss, heat wave…
• Consult your doctor urgently or contact the Samu (15) if you have the following clinical signs, suggestive of lactic acidosis:
  • Repeated vomiting;
  • Diarrhea ;
  • Abdominal pain ;
  • Diffuse muscle cramps and pain;
  • Feeling of malaise associated with severe fatigue;
  • Difficulties in breathing.

For their part, doctors are called upon to be vigilant concerning the signs suggestive of acidosis, the contraindications, the risks of drug interactions and the necessary information for patients on metformin.