Metformin; Uses, Dosage, Side Effects, Drug Interactions

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Metformin is a biguanide hypoglycemic agent used in the treatment of non-insulin-dependent diabetes mellitus not responding to dietary modification. Metformin improves glycemic control by improving insulin sensitivity and decreasing intestinal absorption of glucose. (From Martindale, The Extra Pharmacopoeia, 30th ed, p289)
Metformin is an agent belonging to the biguanide class of antidiabetics with antihyperglycemic activity. Metformin is associated with a very low incidence of lactic acidosis. This agent helps reduce LDL cholesterol and triglyceride levels, and is not associated with weight gain, and prevents the cardiovascular complications of diabetes. Metformin is not metabolized and is excreted unchanged by the kidneys.

Metformin is a biguanide antihyperglycemic agent used for treating non-insulin-dependent diabetes mellitus (NIDDM). It is the first-line medication for the treatment of type 2 diabetes, particularly in people who are overweight. It is also used in the treatment of polycystic ovary syndrome. Limited evidence suggests metformin may prevent the cardiovascular disease and cancer complications of diabetes. It improves glycemic control by decreasing hepatic glucose production, decreasing glucose absorption and increasing insulin-mediated glucose uptake. Metformin may induce weight loss and is the drug of choice for obese NIDDM patients. Use of metformin is associated with modest weight loss.

Mechanism of Action of Metformin

Metformin’s mechanisms of action differ from other classes of oral antihyperglycemic agents. Metformin decreases blood glucose levels by decreasing hepatic glucose production, decreasing intestinal absorption of glucose, and improving insulin sensitivity by increasing peripheral glucose uptake and utilization. These effects are mediated by the initial activation by metformin of AMP-activated protein kinase (AMPK), a liver enzyme that plays an important role in insulin signaling, whole body energy balance, and the metabolism of glucose and fats. Activation of AMPK is required for metformin’s inhibitory effect on the production of glucose by liver cells. Increased peripheral utilization of glucose may be due to improved insulin binding to insulin receptors. Metformin administration also increases AMPK activity in skeletal muscle. AMPK is known to cause GLUT4 deployment to the plasma membrane, resulting in insulin-independent glucose uptake. The rare side effect, lactic acidosis, is thought to be caused by the decreased liver uptake of serum lactate, one of the substrates of gluconeogenesis. In those with healthy renal function, the slight excess is simply cleared. However, those with a severe renal impairment may accumulate clinically significant serum lactic acid levels. Other conditions that may precipitate lactic acidosis include severe hepatic disease and acute/decompensated heart failure.

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Indications of Metformin

  • Diabetes, Type 2
  • Polycystic Ovary Syndrome
  • Diabetes, Type 3c
  • Insulin Resistance Syndrome
  • Female Infertility
  • For use as an adjunct to diet and exercise in adult patients (18 years and older) with NIDDM. May also be used for the management of metabolic and reproductive abnormalities associated with polycystic ovary syndrome (PCOS). Jentadueto is for the treatment of patients when both linagliptin and metformin is appropriate.

Dosage of Metformin

  • Strengths: 500 mg; 750 mg; 850 mg; 1000 mg; 500 mg/5 mL

Diabetes Type 2


  • Initial dose: 500 mg orally twice a day or 850 mg orally once a day
  • Dose titration: Increase in 500 mg weekly increments or 850 mg every 2 weeks as tolerated
  • Maintenance dose: 2000 mg daily in divided doses
  • Maximum dose: 2550 mg/day


  • Initial dose: 500 to 1000 mg orally once a day
  • Dose titration: Increase in 500 mg weekly increments as tolerated
  • Maintenance dose: 2000 mg daily
  • Maximum dose: 2500 mg daily

Pediatric Diabetes Type 2

10 years or older

  • Initial dose: 500 mg orally twice a day
  • Dose titration: Increase in 500 mg weekly increments as tolerated
  • Maintenance dose: 2000 mg daily
  • Maximum dose: 2000 mg daily

Side Effects of Metformin

Most common

More common

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Less common

  • Abnormal stools
  • bad, unusual, or unpleasant (after) taste
  • change in taste
  • difficulty with moving
  • discoloration of the fingernails or toenails
  • flu-like symptoms
  • joint pain
  • rash
  • runny nose
  • sneezing
  • stuffy nose
  • swollen joints

Drug Interactions of Metformin

Metformin may interact with following drugs, supplements & may decrease the efficacy of the drug

Pregnancy & Lactation of Metformin

FDA Pregnancy Category B


This medication should not be used during pregnancy. If you become pregnant while taking this medication, contact your doctor immediately.


Metformin is believed to pass into breast milk. This medication should not be used if you are breastfeeding.



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