Metformin

What is it?

According to MedlinePlus, metformin is a drug of the biguanide class that "reduces the amount of glucose you absorb from your food and the amount of glucose your liver makes" and increases the body's response to insulin. It is not used for type 1 diabetes according to this page.

The NIDDK says: "Most people with type 2 diabetes start with metformin tablets, which are also available as a liquid, and it helps the liver produce less glucose and helps the body use insulin better". It adds that combining two or three types of diabetes drugs may lower glucose better than one drug.

The drug is available in several forms: solution, regular tablets and extended-release tablets (MedlinePlus), and as tablets, liquid or powder (NHS). Brand names MedlinePlus mentions include Glucophage, Glumetza, Fortamet and Riomet, as well as products combined with other diabetes drugs.

Uses

According to MedlinePlus: to treat type 2 diabetes, alone or with other drugs including insulin.

According to the NHS: it is prescribed for type 2 diabetes (alone or with other drugs), for gestational diabetes, for symptoms of polycystic ovary syndrome (which the NHS abbreviates as PMOS), and for type 1 in combination with insulin.

According to the FDA label (extended-release tablets): an adjunct to diet and exercise to improve blood sugar control in adults with type 2 diabetes. Indications differ between bodies and products, and the doctor decides what suits your condition.

How it is used

According to MedlinePlus: the solution is taken with meals once or twice a day, regular tablets with meals twice or three times a day, and extended-release tablets once a day with the evening meal. Extended-release tablets are swallowed whole without splitting, chewing or crushing.

MedlinePlus notes that doctors usually start with a low dose then increase it gradually at intervals of one to two weeks. The dose and its duration are decided by the doctor, and no numbers are given here.

According to the NHS: tablets are swallowed whole with a little water without crushing or chewing; the powder is mixed with water before drinking; and the supplied measure or syringe is used for the liquid. The drug is usually taken one to three times a day with food, and treatment may be long term with follow-up.

MedlinePlus recommends continuing the drug even when you feel better, and following the doctor's or dietitian's recommendations on diet and exercise. The NHS states to eat normally during treatment.

Side effects

Common effects according to MedlinePlus: diarrhoea, nausea, stomach discomfort, gas, indigestion, constipation, weakness, change in taste, headache, flushing, nail changes, muscle pain, rash.

According to the NHS: common ones are nausea, vomiting, diarrhoea, abdominal pain, loss of appetite, change in taste and vitamin B12 deficiency (which may cause fatigue). Most ease within weeks, and the pharmacist is consulted if they are troublesome.

Rare serious effects according to the NHS: lactic acidosis (excess acid in the blood), severe hypersensitivity (swelling of the throat or tongue, itchy rash and difficulty breathing), and hepatitis (yellowing of the skin or eyes).

MedlinePlus notes that the shell of extended-release tablets may appear empty in the stool and this is normal. It notes that chest pain calls for telling the doctor immediately.

Warnings and precautions

Lactic acidosis: according to MedlinePlus "metformin may rarely cause a serious life-threatening condition called lactic acidosis". It asks you to tell the doctor if you have kidney disease or are over 65, or have had a heart attack or stroke, diabetic ketoacidosis or coma, or have heart or liver disease.

Warning symptoms according to MedlinePlus: tiredness, weakness or severe discomfort, nausea, vomiting, abdominal pain, reduced appetite, deep rapid breathing or shortness of breath, dizziness, fast or slow heartbeat, muscle pain, or feeling cold. It directs to stop the drug and call the doctor immediately if they appear, and the NHS states that lactic acidosis calls for emergency care.

According to the FDA label: the boxed warning states that cases of metformin-associated lactic acidosis have led to death, low body temperature and low blood pressure, and that risk factors include kidney impairment, some drugs, age 65 and over, contrast studies, surgery, hypoxic states, excessive alcohol intake and liver impairment. It states that the drug is contraindicated in metabolic acidosis including diabetic ketoacidosis.

Alcohol: MedlinePlus says drinking increases the risk of lactic acidosis or may lower blood sugar, and the NHS states to limit alcohol. The FDA label notes that alcohol potentiates the effect of metformin on lactate metabolism.

Situations it is advisable to discuss with the doctor because the drug may not suit them according to the NHS: a previous allergy or serious side effect, kidney and liver problems, severe infection (chest or kidney), heart failure, and excessive alcohol use. The FDA label states to avoid the drug with clinical or laboratory evidence of liver disease.

Dehydration: the NHS advises consulting the pharmacist in case of vomiting, diarrhoea or fever because of the risk of dehydration. The FDA label notes that withholding food and fluids during surgery or procedures may increase the risk of fluid depletion.

Low blood sugar: according to the FDA label its risk increases when combined with insulin or drugs that stimulate its release, and the doses may need adjustment, which the doctor decides.

The NHS notes that the drug does not usually affect driving unless it causes dizziness.

Interactions

According to MedlinePlus: drugs that increase the risk of lactic acidosis with metformin include acetazolamide, dichlorphenamide, methazolamide, topiramate and zonisamide. Tell the doctor and pharmacist about all the medicines, vitamins, supplements and herbs you take.

According to the NHS: avoid combining, or consult the doctor, regarding diuretics, non-steroidal anti-inflammatory drugs (such as ibuprofen and diclofenac) and some blood pressure drugs.

The FDA label notes that some drugs are linked to lactic acidosis among the risk factors, and the details are in the full leaflet of your product.

Monitoring

According to the FDA label: the estimated glomerular filtration rate (eGFR) is measured at least once a year in all patients, the drug is not used if the eGFR is below 30 ml/min/1.73 m², benefit and risk are assessed if it falls below 45, and starting treatment between 30 and 45 is not recommended. The doctor is the one who applies this. Labels and guidelines differ, so what counts is your laboratory's report and your doctor's interpretation.

The FDA label mentions measuring blood parameters annually and vitamin B12 every two to three years with correction of any deficiency, and the NHS agrees that B12 deficiency is a possible effect.

MedlinePlus says: monitor blood sugar at home according to the doctor's instructions.

Special situations

Pregnancy: according to MedlinePlus tell your doctor if you are pregnant, planning pregnancy or breastfeeding, and call them if you become pregnant during treatment. The NHS notes that it can be taken in pregnancy after consulting the doctor, because blood sugar control prevents the risk of miscarriage, and that breastfeeding is allowed because it passes in tiny amounts in milk. The FDA label notes that the limited data are not enough to determine the risk and that the drug is present in breast milk.

Children: the NHS notes that it is suitable from age 10 and for most adults, whereas the FDA label says safety and effectiveness in children have not been established for that product.

Older people: the FDA label states caution in choosing the dose and assessing the kidneys more often.

Contrast imaging and surgery: according to MedlinePlus tell your doctor before any X-ray in which a dye is injected, especially with heavy alcohol drinking, liver disease or heart failure, and before dental or major surgery; you may be asked to stop the drug and wait at least 48 hours before resuming it. The FDA label notes that stopping at the time of the procedure may be needed in cases including moderate kidney impairment and intra-arterial contrast, with eGFR reassessed after 48 hours. The decision is the doctor's.

MedlinePlus advises carrying a card or bracelet identifying diabetes.

Common situations

A missed dose according to MedlinePlus: take it when remembered, and if the time for the next dose is near, skip it and resume the usual plan, and do not double the dose. The NHS elaborates: for those taking it once a day, take it when remembered unless the next is near, and for those taking it more than once the missed dose is skipped, with no doubling.

Overdose: the NHS says an overdose may be dangerous and advises seeking medical help immediately. MedlinePlus mentions calling poison control or the ambulance in case of collapse, seizure or difficulty breathing.

Storage according to MedlinePlus: in its original container tightly closed, at room temperature, away from light, heat and moisture (not in the bathroom), and out of reach of children.

Common questions