• Decreases hepatic gluconeogenesis production
  • Decreases intestinal absorption of glucose
  • improves insulin sensitivity by increasing peripheral glucose uptake and utilization
  • Metformin improve glucose utilization in skeletal muscle and adipose tissue by increasing cell membrane glucose transport.
    • This effect may be due to improved binding of insulin to insulin receptors since metformin is not effective in diabetics without some residual functioning pancreatic islet cells
  • rarely causes hypoglycemia since it does not significantly change insulin concentrations




-----------------------------------------Information from Clinical Pharmacology--------------------------
Mechanism of Action: Metformin is an antihyperglycemic agent that improves glucose tolerance, lowering both basal and postprandial plasma glucose with mechanisms different from other classes of oral antidiabetic agents. Metformin decreases hepatic gluconeogenesis production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may actually decrease. Metformin improve glucose utilization in skeletal muscle and adipose tissue by increasing cell membrane glucose transport. This effect may be due to improved binding of insulin to insulin receptors since metformin is not effective in diabetics without some residual functioning pancreatic islet cells.[24568] Unlike the sulfonylureas, metformin rarely causes hypoglycemia since it does not significantly change insulin concentrations. An important distinction is that sulfonylureas increase insulin secretion thus making them useful in non-obese patients with type 2 diabetes while metformin improves insulin resistance, a common pathophysiologic finding in obese patients with type 2 diabetes.[24568] Metformin causes a 10—20% decrease in fatty-acid oxidation and a slight increase in glucose oxidation. Unlike phenformin, metformin does not inhibit the mitochondrial oxidation of lactate unless plasma concentrations of metformin become excessive (i.e., in patients with renal failure) and/or hypoxia is present.[24438]

Clinically, metformin lowers fasting and postprandial hyperglycemia. The decrease in fasting plasma glucose is approximately 25—30%. Unlike oral sulfonylureas, metformin rarely causes hypoglycemia. Thus, metformin demonstrates more of an antihyperglycemic action than a hypoglycemic action. Metformin does not cause weight gain and in fact, may cause a modest weight loss due to drug-induced anorexia. Metformin also decreases plasma VLDL triglycerides resulting in modest decreases in plasma triglycerides and total cholesterol. Patients receiving metformin show a significant improvement in hemoglobin A1c, and a tendency toward improvement in the lipid profile, especially when baseline values are abnormally elevated.

Insulin resistance is a primary cause of polycystic ovarian syndrome (PCOS). In PCOS patients, metformin reduces insulin resistance and lowers insulin levels, which lowers serum androgen concentrations, restores normal menstrual cycles and ovulation, and may help to resolve PCOS-associated infertility. Metformin, when administered to lean, overweight, and moderately obese women with PCOS, has been found to significantly reduce serum leuteinizing hormone (LH) and increase follicle stimulating hormone (FSH) and sex hormone binding globulin (SHBG). Serum testosterone concentrations were also found to decrease by approximately 50%.