METFORMIN

Biguanide oral antidiabetic medicine. It works by decreasing gluconeogenesis and by increasing peripheral utilisation of glucose.

Since it acts only in the presence of endogenous insulin it is effective only if there are some residual functioning pancreatic islet cells.

Dosage Forms

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Tablet

500 mg
1000 mg

Uses

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  • Type 2 diabetes mellitus [monotherapy or in combination with other antidiabetic drugs (including insulin)]

Dose and Duration

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Type II diabetes
BY MOUTH USING IMMEDIATE-RELEASE MEDICINES

Child 10–17 years (specialist use only) Initially 500 mg once daily, dose to be adjusted according to response at intervals of at least 1 week, maximum daily dose to be given in 2–3 divided doses.
Maximum 2g per day

Adult: Initially 500 mg once daily for at least 1 week, dose to be taken with breakfast, then 500 mg twice daily for at least 1 week, dose to be taken with breakfast and evening meal,then 500 mg 3 times a day,dose to be taken with breakfast, lunch and evening meal.
Maximum 2g per day

Child 8–10 years: initially 200 mg once daily adjusted according to response at intervals of at least 1 week (max 2 g daily in 2–3 divided doses)

BY MOUTH USING MODIFIED-RELEASE MEDICINES

Adult: Initially 500 mg once daily, then increased if necessary up to 2 g oncedaily, dose increased gradually, every 10–15days, dose to be taken with evening meal, alternatively increased to 1 g twice daily, dose to betaken with meals, alternative dose only to be used if control not achieved with once daily dose regimen.
If control still not achieved then change to standard release tablets

Type 2 diabetes mellitus [reduction in risk or delay of onset]
BY MOUTH USING MODIFIED-RELEASE MEDICINES

Adult 18–74 years: Initially 500 mg once daily, then increased if necessary up to 2g once daily, dose increased gradually, every 10–15days, dose to be taken with evening meal, for further information on risk factors—consult product literature

Polycystic ovary syndrome
BY MOUTH USING IMMEDIATE-RELEASE MEDICINES

Adult (initiated by a specialist): Initially 500 mg once daily for 1 week, dose to be taken with breakfast, then 500 mg twice daily for 1 week, dose to be taken with breakfast and evening meal, then 1.5–1.7 g daily in 2–3 divided doses

Contraindications

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  • Acute metabolic acidosis (including lactic acidosis and diabetic ketoacidosis)
  • General anaesthesia
  • Iodine-containing x-ray contrast media
  • Moderate to severe renal impairment
  • Alcohol dependency
  • Disease that may cause tissue hypoxia (e.g. heart failure, respiratory failure, recent myocardial infarction, shock)

Side Effects

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Common or very common

  • Nausea, vomiting, diarrhoea, abdominal pain, taste disturbance
  • Decreased vitamin B12 absorption
  • Itching
  • Lactic acidosis

Rare or very rare

  • Hepatitis
  • Decreased vitamin B12 absorption hence Vitamin B12 deficiency
  • Skin reactions like itching
  • Lactic acidosis

Patient Instructions

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  • Continue diet restrictions and exercise recommendations
  • Always take metformin with meals
  • Gastrointestinal side - effects are most frequent during treatment initiation and usually resolve spontaneously. A slow increase in dose may improve tolerability.
  • Patients and their carers should be informed of the risk of lactic acidosis and told to seek immediate medical attention if symptoms such as dyspnoea, muscle cramps, abdominal pain, hypothermia, or asthenia occur

Pregnancy

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  • Can be used in pregnancy for both pre existing and gestational diabetes.
    Women with gestational diabetes should discontinue treatment after giving birth.

Breast-feeding

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  • Maybe used during breast-feeding in women with pre-existing diabetes.

⚠️ Caution

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  • May cause lactic acidosis in renal impairment.

    Avoid if eGFR is less than 30mL/minute/1.73m2.

  • Determine renal function before treatment and at least once a year during treatment
  • Suspend metformin on morning of surgery and restart when renal function returns to normal
  • Iodinated contrast media may cause kidney failure, which can increase the risk of lactic acidosis with metformin. Suspend metformin prior to the test; restart no earlier than 48 hours after the test and renal function has returned to normal
  • Insulin is always required in medical and surgical emergencies e.g. during infections
  • During pregnancy, it is preferable to use insulin so as to achieve as normal as possible blood glucose concentrations