Metformin precautions

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

List of precautions

Monitoring of renal function

Concomitant Medications

Hypoxic states

Surgical procedures

Alcohol intake

Impaired hepatic function

Vitamin B12 levels

Change in clinical status of patients with previously controlled type 2 diabetes

Hypoglycemia

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Monitoring of renal function

Metformin is known to be substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of impairment of renal function. Thus, patients with serum creatinine levels above the upper limit of normal for their age should not receive Metformin. In patients with advanced age, Metformin should be carefully titrated to establish the minimum dose for adequate glycemic effect, because aging is associated with reduced renal function. In elderly patients, particularly those ≥ 80 years of age, renal function should be monitored regularly and, generally, Metformin should not be titrated to the maximum dose. Return to top

Concomitant Medications

Use of concomitant medications that may affect renal function or metformin disposition—Concomitant medication(s) that may affect renal function or result in significant hemodynamic change or may interfere with the disposition of metformin, such as cationic drugs that are eliminated by renal tubular secretio should be used with caution. Return to top

Hypoxic states

Cardiovascular collapse (shock) from whatever cause, acute congestive heart failure, acute myocardial infarction and other conditions characterized by hypoxemia have been associated with lactic acidosis and may also cause prerenal azotemia. When such events occur in patients on Metformin therapy, the drug should be promptly discontinued. Return to top

Surgical procedures

Metformin therapy should be temporarily suspended for any surgical procedure (except minor procedures not associated with restricted intake of food and fluids) and should not be restarted until the patient's oral intake has resumed and renal function has been evaluated as normal. Return to top

Alcohol intake

Alcohol is known to potentiate the effect of metformin on lactate metabolism. Patients, therefore, should be warned against excessive alcohol intake, acute or chronic, while receiving Metformin. Return to top

Impaired hepatic function

Since impaired hepatic function has been associated with some cases of lactic acidosis, Metformin should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Return to top

Vitamin B12 levels

In controlled clinical trials of Metformin of 29 weeks duration, a decrease to subnormal levels of previously normal serum Vitamin B12 levels, without clinical manifestations, was observed in approximately 7% of patients. Such decrease, possibly due to interference with B12 absorption from the B12-intrinsic factor complex, is, however, very rarely associated with anemia and appears to be rapidly reversible with discontinuation of Metformin or Vitamin B12 supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on Metformin and any apparent abnormalities should be appropriately investigated and managed. Return to top

Change in clinical status of patients with previously controlled type 2 diabetes

A patient with type 2 diabetes previously well controlled on Metformin who develops laboratory abnormalities or clinical illness (especially vague and poorly defined illness) should be evaluated promptly for evidence of ketoacidosis or lactic acidosis. Evaluation should include serum electrolytes and ketones, blood glucose and, if indicated, blood pH, lactate, pyruvate, and metformin levels. If acidosis of either form occurs, Metformin must be stopped immediately and other appropriate corrective measures initiated. Return to top

Hypoglycemia

Hypoglycemia does not occur in patients receiving Metformin alone under usual circumstances of use, but could occur when caloric intake is deficient, when strenuous exercise is not compensated by caloric supplementation, or during concomitant use with other glucose-lowering agents (such assulfonylure as and insulin) or ethanol. Return to top

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Adapted from the FDA Package Insert.