BMA Concise Guide to Medicine & Drugs

Metformin

Brand names Glucophage, Glucophage SR

Used in the following combined preparations Avandamet, Competact, Eucreas, Janumet, Komboglyze, Vipdomet, Xigduo

QUICK REFERENCE

Drug group Drug for diabetes

Overdose danger rating High

Dependence rating Low

Prescription needed Yes

Available as generic Yes

GENERAL INFORMATION

Metformin is an antidiabetic drug used to treat Type 2 diabetes, in which some insulin is still produced by the pancreas. The drug reduces blood sugar levels by delaying absorption of glucose, reducing glucose production in the liver, and helping your body respond better to its own insulin so that cells take up glucose more effectively from the blood. Metformin is used in conjunction with a good diet and exercise. It can be given with insulin or other antidiabetic drugs but is often used on its own to treat people with Type 2 diabetes who are obese. Metformin is also used in the treatment of polycystic ovarian syndrome.

INFORMATION FOR USERS

Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses 2–3 x daily with food.

Adult dosage range 1.5–3g daily with a low dose at the start of the treatment.

Onset of effect Within 2 hours. It may take 2 weeks to achieve control of diabetes.

Duration of action 8–12 hours.

Diet advice An individualized low-fat, low-sugar diet must be maintained in order for the drug to be fully effective. Follow your doctor’s advice.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose Take as soon as you remember. If your next dose is due within 2 hours, take a single dose now and skip the next.

Stopping the drug Do not stop taking the drug without consulting your doctor; stopping the drug may lead to worsening of the underlying condition.

OVERDOSE ACTION

Seek immediate medical advice in all cases. Take emergency action if seizures or loss of consciousness occur.

POSSIBLE ADVERSE EFFECTS

A metallic taste in the mouth and minor gastrointestinal symptoms, such as nausea, vomiting, and appetite loss, are common and are often helped by taking the drug with food. Metformin may also cause diarrhoea, but this usually settles after a few days of treatment. Sometimes, the drug may cause dizziness, confusion, weakness, sweating, or a rash; if these occur, you should contact your doctor. The most serious side effect is a potentially fatal build-up of lactic acid in the blood. This is very rare and usually occurs only in diabetics with impaired kidney function.

INTERACTIONS

General note A number of drugs reduce the effects of metformin. These include corticosteroids, oestrogens, and diuretics. Other drugs, notably monoamine oxidase inhibitors (MAOIs) and beta blockers, increase its effects.

Warfarin Metformin may increase the effect of this anticoagulant drug. The dosage of warfarin may need to be adjusted accordingly.

SPECIAL PRECAUTIONS

Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You have heart failure.

· You are a heavy drinker.

· You are taking other medicines.

Pregnancy Not usually prescribed. Insulin is usually substituted because it provides better diabetic control during pregnancy. Discuss with your doctor.

Breast-feeding Safety not established. Discuss with your doctor.

Infants and children Not recommended under 10 years.

Over 60 Increased likelihood of adverse effects. Reduced dose may therefore be necessary.

Driving and hazardous work Usually no problems. Avoid such activities if you have warning signs of low blood sugar.

Alcohol Avoid. Alcohol increases the risk of low blood sugar, and can cause coma by increasing the acidity of the blood.

Surgery and general anaesthetics Surgery may reduce the response to this drug. Notify your doctor that you are diabetic before any surgery; insulin treatment may need to be substituted. Tell your doctor if you are to have a contrast X-ray; metformin should be stopped before the procedure.

PROLONGED USE

Prolonged treatment with metformin can deplete reserves of vitamin B12, and this may rarely cause anaemia.

Monitoring Regular checks on kidney function and on blood sugar control are usually required. Vitamin B12 levels may also be checked annually.