Patients with impaired hepatic function or alcoholism should not receive the drug as lactate metabolism is decreased. In those undergoing tests with intravenous dye, metformin should be discontinued 6 hours prior to the injection of the dye and 48 hours after the procedure, with re-initiation when renal function returns to baseline. The usual dosage is 850 mg twice daily. As a result, strict adherence to contraindications and a knowledge of conditions that may predispose the patient to lactic acidosis are essential. Metformin should be avoided in any condition that may result in metformin accumulation or increased peripheral lactateproduction.
Renal impairment is an absolute contraindication, as is acute or chronic metabolic acidosis.
Patients with hepatic disease may have reduced hepatic lactate clearance, and hence metformin should generally be avoided. In the event of such a condition, metformin should be discontinued. Metformin should only be restarted after normal renal function has been confirmed. Metformin should also be avoided in patients with a history of chronic alcohol abuse as alcohol may potentiate the effect of metformin on lactate metabolism. Metformin works by suppressing basal hepatic glucose production and enhancing insulin sensitivity in muscle.