Indications
- Type 2 diabetes in adults and children aged 10 years and over, alone or with other diabetes medicines or insulin, together with diet and exercise.
- Doctors may also use it for prediabetes (blood sugar higher than normal but not yet diabetes) and for polycystic ovary syndrome (PCOS).
How It Works
Metformin lowers blood sugar mainly by reducing the amount of sugar the liver releases into the blood. It also helps the body respond better to its own insulin and slightly reduces sugar absorption from the gut. On its own it rarely causes low blood sugar.
Dosage and Administration
- Adults, standard tablets: usually started at 500 mg once or twice a day with meals. The doctor increases the dose slowly, every 1 to 2 weeks, to reduce stomach upset. A common dose is 1,000 to 2,000 mg a day divided between meals. The maximum depends on the product and is decided by the doctor.
- Extended-release tablets: usually taken once a day with the evening meal; swallow whole, do not crush or chew.
- Children aged 10 and over: as prescribed.
- Lower doses are used when kidney function is reduced.
- Take with or right after food. Do not stop taking it without speaking to your doctor.
Interactions
- X-ray dyes containing iodine (used for some scans): metformin is usually stopped before or at the time of the scan and restarted after 48 hours if kidney function is normal.
- Alcohol raises the risk of lactic acidosis; avoid heavy drinking.
- Cimetidine, Dolutegravir, Ranolazine, Topiramate and Acetazolamide can increase its level or the risk of side effects.
- Insulin and sulfonylureas (such as Gliclazide) can cause low blood sugar when used with it.
- Corticosteroids and some diuretics can raise blood sugar.
Contraindications
- Allergy to metformin.
- Severe kidney impairment.
- Diabetic ketoacidosis or other acid build-up in the blood.
- Severe infection, severe dehydration, shock, or conditions that lower oxygen in the body (such as severe heart or lung failure or a recent heart attack).
- Severe liver disease or alcohol dependence.
Side Effects
Common, especially at the start: nausea, diarrhoea, stomach pain, gas, loss of appetite and a metallic taste. These usually settle within a few weeks. Long-term use can lower vitamin B12 levels.
Get urgent medical help for signs of lactic acidosis (a rare but serious acid build-up in the blood):
- Severe vomiting or stomach pain, muscle cramps or pain.
- Unusual tiredness or weakness, fast or deep breathing.
- Feeling cold, dizziness, or a slow or irregular heartbeat.
Also seek help for severe allergic reactions such as swelling of the face or difficulty breathing.
Pregnancy and Lactation
Metformin may be used in pregnancy only on a doctor’s advice; insulin is often preferred, and blood sugar control is very important. Small amounts pass into breast milk; it is generally considered acceptable during breastfeeding when the doctor advises it.
Precautions and Warnings
- Kidney function is checked before starting and at least once a year.
- Stop and contact your doctor if you have severe vomiting, diarrhoea or dehydration, or before surgery.
- Vitamin B12 levels may be checked with long-term use, especially if you get numbness or tingling.
- If taken with insulin or sulfonylureas, learn the signs of low blood sugar (shaking, sweating, hunger, confusion).
Overdose
Large overdoses can cause lactic acidosis, which is a medical emergency. Go to the nearest hospital straight away and take the pack with you.
Therapeutic Class
Oral antidiabetic medicine; biguanide.
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.