Metformin (pronounced MET -FOR-MIN), is the most common medication, and often the first medication prescribed, for people living with type 2 diabetes. It is prescribed in various strengths, and release types, and in combination with other medications.

The drug

The chemical name for metformin is dimethylbiguanide and common brand names include Diabex, Diaformin, Metex and Glucophage. Metformin is the only medication in a group of medications called biguanides, and it is unique in the way it works in the body.

The herb and the history

The herb Galega officinalis, also known as Goat’s Rue, was a traditional herbal medicine used in Europe. Galega officinalis is rich in guanidine and in 1918 this was found to lower blood glucose levels.

Chemicals were synthesized from guanidine and drugs produced. These drugs called phenformin and buformin were used in the 1920s and 1930s to treat diabetes but were discontinued due to toxicity and side effects such as risk of lactic acidosis. Metformin was synthesized at this same time but was not as potent in lowering blood glucose levels. It was set aside and not tested further.

In 1957, a physician called Jean Sterne rediscovered metformin, and began to use it to treat type 2 diabetes. Metformin became noticed and was then marketed for sale under the brand name Glucophage in the United Kingdom in 1958, Canada in 1972, Australian in 1992 the US in 1995.

How it works

Metformin works in the body by reducing both basal (long-acting) and postprandial (after meals) plasma glucose. It does not stimulate insulin secretion and in monotherapy (use of one medication), does not cause hypoglycaemia.

Metformin may act via three mechanisms:

• It reduces the output of glucose from the liver
• In muscle it increases insulin sensitivity, improving glucose uptake into the muscle for use
• Delays glucose absorption in the intestines.

Formulations

In Australia, metformin is available in strengths of 500 milligrams (mg), 850mg and 1000mg.

Metformin is available in immediate release and extended release formulations. Immediate release formulations mean that as soon as you swallow the tablet, all the medication will dissolve and be absorbed into your blood stream and starts to have an effect. In extended release formulations, the medication starts to release the medication and is absorbed into your blood stream slowly over the course of time, leading to more consistent blood levels of the medication.

Immediate release formulations will be labelled as metformin and the strength (for example metformin 500 milligrams (mg)).

Extended release medications will be labelled as metformin 500mg XR or MR. XR stands for extended release and MR stands for modified release. These are both slow release formulations.

Extended release medications are film coated and should not be crushed or chewed.

How to take it

The timeframe of when your doctor will want you to take your medication may change between extended release and immediate release tablets.

Metformin tablets are usually taken with the evening meal. Taking your tablets with a meal will help reduce stomach upset.

Most often metformin will be prescribed to be taken once or twice daily.

Side effects

Metformin has a range of common gastrointestinal side effects. These include:

• upset stomach
• bloating and cramping
• diarrhoea
• nausea and vomiting.

Everyone is individual and while some people may not experience any side effects, the above side effects can be quite common. If you do experience these side effects, you can minimize them by taking your tablets with a meal. The side effects usually subside within a few weeks.

Metformin can also cause vitamin B12 deficiency in up to 30% of people who take it.

Metformin has a rare side effect associated with it called lactic acidosis. This side effect can cause muscle cramps, stomach pain, feeling weak and breathing issues. If you experience these side effects, you need to go to hospital straight away.

Surgery and scans

It is important that you tell your doctor if you are going to hospital to have surgery. Metformin is often stopped for major surgery. You require a scan at hospital such as an X-ray or CT scan where contrast media (which may contain iodine) is used. Having these procedures while taking metformin can affect your kidneys. You should advise when booking your procedure that you are taking metformin and follow their instructions.

Generally, metformin is a safe and effective medication used in the treatment of type 2 diabetes. If you have any concerns about metformin, talk to you doctor or pharmacist.

By Alison Crow, Pharmacist and CDE