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
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
Adapted from the FDA Package Insert.