Metformin: The Most Popular Biguanide Explained

Metformin belongs to Biguanides, a class of oral antidiabetic drugs that are used to treat type 2 diabetes mellitus. The most commonly used biguanide is metformin.


Mechanism of action

  • It works by a number of mechanisms, including:
    • Inhibition of gluconeogenesis: Metformin inhibits the activity of the enzyme gluconeogenic phosphoenolpyruvate carboxykinase (PEPCK), which is involved in the production of glucose from non-carbohydrate sources. This means that less glucose is produced by the liver, which helps to lower blood sugar levels.
    • Increased insulin sensitivity: Metformin increases the sensitivity of muscle and fat cells to insulin. This means that these cells are better able to take up glucose from the blood, even in the presence of high blood sugar levels. This also helps to lower blood sugar levels.
    • Activation of AMPK: Metformin activates AMP-activated protein kinase (AMPK), which is a cellular sensor of energy levels. AMPK activates a number of genes that are involved in glucose metabolism, including the gene for GLUT4, which is a protein that helps glucose move into cells.
    • Reduced intestinal glucose absorption: Metformin may also reduce intestinal glucose absorption. This is thought to be due to the inhibition of sodium-glucose cotransporter 1 (SGLT1), which is a protein that transports glucose from the small intestine into the bloodstream.



Biguanides are absorbed from the gastrointestinal tract and distributed throughout the body. They are not metabolized in the liver and are excreted unchanged in the urine.


Biguanides have a number of pharmacodynamic effects, including:

  • Hypoglycemic effect: Biguanides lower blood sugar levels by a combination of mechanisms, including inhibition of gluconeogenesis and increased insulin sensitivity.
  • Weight loss: Biguanides can cause weight loss, which may be beneficial for people with type 2 diabetes.
  • Anti-inflammatory effect: Biguanides have anti-inflammatory effects, which may help to protect against the development of complications of diabetes, such as heart disease and kidney disease.
  • Anti-cancer effect: Biguanides have anti-cancer effects, which may help to prevent the development of certain types of cancer, such as breast cancer and colon cancer.

Here are some of the therapeutic uses of metformin

  • Type 2 diabetes: Metformin is the first-line drug for the treatment of type 2 diabetes. It is effective in lowering blood sugar levels and preventing complications of diabetes, such as heart disease, stroke, and kidney disease.
  • Polycystic ovary syndrome (PCOS): Metformin is used to treat PCOS, a condition that affects women of childbearing age. PCOS can cause irregular periods, infertility, and excessive hair growth. Metformin helps to regulate ovulation and improve fertility in women with PCOS.
  • Gestational diabetes mellitus: Metformin is used to treat gestational diabetes mellitus, a type of diabetes that occurs during pregnancy. Gestational diabetes can cause complications for both the mother and the baby. Metformin helps to control blood sugar levels and prevent complications of gestational diabetes.
  • Prevention of type 2 diabetes: Metformin can be used to prevent type 2 diabetes in people who are at high risk for the disease. This includes people who are overweight or obese, have a family history of diabetes, or have other risk factors for diabetes.

Adverse effects

The most common side effects of biguanides are:

  • Nausea: This is the most common side effect of biguanides. It usually goes away on its own after a few days.
  • Vomiting: This is less common than nausea, but it can also occur.
  • Diarrhea: This is also less common than nausea and vomiting, but it can be more serious. If you experience diarrhea, it is important to tell your doctor.
  • Weight loss: Biguanides can cause weight loss, which may be beneficial for people with type 2 diabetes. However, it can also be a side effect that some people do not want.
  • Lactic acidosis: This is a rare but serious side effect of biguanides. It is important to be aware of the signs and symptoms of lactic acidosis and to seek medical attention immediately if you experience any of them. The signs and symptoms of lactic acidosis include:
    • Muscle pain
    • Weakness
    • Rapid breathing
    • Confusion
    • Stomach pain
    • Dizziness
    • Pale skin


Biguanides can interact with other drugs, so it is important to tell your doctor about all the medications you are taking, including over-the-counter medications and herbal supplements. Some of the drugs that can interact with biguanides include:

  • Alcohol
  • Metformin
  • Sulfonylureas
  • Thiazolidinediones
  • Insulin

Dosage and administration

The dosage of biguanides is individualized. The usual starting dose is 500 mg once or twice daily. The dose may be increased gradually up to a maximum of 2000 mg daily.

Biguanides are typically taken with food to reduce the risk of side effects. They should also be taken with plenty of fluids.


Patients taking biguanides should be monitored for the development of lactic acidosis. This is a serious condition that can be fatal. Patients should also be monitored for kidney function and liver function.

Patient Education

Patients taking biguanides should be aware of the signs and symptoms of lactic acidosis. These include nausea, vomiting, diarrhea, muscle pain, and shortness of breath. Patients should also be aware of the need to avoid alcohol while taking biguanides.

Patients should contact their doctor immediately if they experience any of the above symptoms.

I hope this more detailed pharmacology of biguanides is helpful. Please let me know if you have any other questions.

Disclaimer: This article is for informational purposes only and should not be considered as medical advice.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always seek the advice of a healthcare provider with any questions regarding a medical condition.

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