Metformin
A biguanide tablet for type 2 diabetes that lowers liver glucose output without weight gain or, used alone, hypoglycemia.
Drug card
- Class
- Biguanide
- How it works
- Reducing the liver's glucose output and improving insulin sensitivity
- Used for
- Type 2 diabetes (adults and children aged 10 and over)
- Delaying type 2 diabetes in high-risk prediabetes
- Diabetes in pregnancy (gestational diabetes)
- Polycystic ovary syndrome (PCOS)
- Known for
- Diarrhea
- Low vitamin B12 with long-term use
- Lactic acidosis (rare but can be fatal)
- Its name
- -formin means a biguanide (metformin type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does metformin work?
Metformin lowers fasting and after-meal glucose by reducing glucose production in the liver, raising glucose uptake by muscle and cutting absorption from the gut. It activates the enzyme AMPK (AMP-activated protein kinase), though how its several effects fit together is not fully settled. It is not metabolized and is cleared unchanged by the kidneys.
Uses
What is metformin used for?
- Type 2 diabetes (adults and children aged 10 and over)
- Delaying type 2 diabetes in high-risk prediabetes
- Diabetes in pregnancy (gestational diabetes)
- Polycystic ovary syndrome (PCOS)
Side effects
Side effects of metformin
- DiarrheaKnown for
- Low vitamin B12 with long-term useKnown for
- Lactic acidosis (rare but can be fatal)Known forSerious
- Nausea and vomiting
- Abdominal pain or discomfort
- Bloating and wind
- Indigestion
- Loss of appetite
- Change in taste
- Weakness and tiredness
- Liver inflammation (hepatitis), very rareSerious
- Hypoglycemia when combined with insulin or sulfonylureas
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated when eGFR is below 30 and in metabolic acidosis, including diabetic ketoacidosis.
- Withhold around iodinated contrast imaging in people at risk, and during surgery or a dehydrating illness.
- Topiramate and other carbonic anhydrase inhibitors, and OCT2/MATE blockers such as cimetidine, raise lactic acidosis risk.
Good to know: Stomach upset is common at the start and usually settles; body weight stays stable or falls a little.
Remember it
A way to remember it
LIVER
- L
- Lactic acidosis
- I
- Iodinated contrast: withhold around scans
- V
- Vitamin B12 deficiency
- E
- Excreted unchanged by the kidneys: avoid if eGFR is below 30
- R
- Reduces glucose output from the liver
Biguanides work mainly on the liver; the five letters give their action, their rare but deadly risk and the rules that prevent it.
Written for biofideX
Its name
-formin means biguanide (metformin type)
Metformin, phenformin and buformin are biguanides, named after phenformin. Metformin is the one in everyday use.
- Every drug name stem
Its class
Biguanides
Biguanides lower blood glucose mainly by cutting glucose production in the liver. They also raise glucose uptake by muscle, partly by improving insulin action, and reduce glucose absorption from the gut. They do not stimulate insulin release, so alone they do not cause hypoglycemia. They act in several ways at once, and which of these matters most is not fully settled.
Easily mixed up with sulfonylureas and thiazolidinediones.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Metformin hydrochloride tablets: label (DailyMed)
- Metformin 500 mg prolonged-release tablets: SmPC (emc)
- Metformin (NHS)
- Metformin (NCI Thesaurus)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Diabetes
Metformin is one of 14 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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