Pharmacology · Class
Biguanides !
Oral glucose-lowering drugs that make the liver release less glucose. Metformin is the only one still in wide use.
Updated 2026-11-01
What they are
Guanidine-derived oral drugs for type 2 diabetes. They lower glucose without raising insulin secretion.
Mechanism of action
Biguanides accumulate in liver cells and mildly inhibit mitochondrial complex I. The cell's energy charge falls (less ATP, more AMP), AMPK is activated and hepatic gluconeogenesis drops. Which of these effects matters most, and how much the gut contributes, is still debated.
Target: Mitochondrial respiratory chain, complex I (with AMPK activation downstream)
Drugs in this class
Others in the class
- phenformin (withdrawn in most countries because of lactic acidosis)
- buformin
Test yourself
Think of the answer, then tap the question to see it.
Why was phenformin withdrawn while metformin remained in use?
Phenformin caused lactic acidosis far more often. Metformin is more polar, enters mitochondria less avidly and carries a much lower, though real, risk.
Do biguanides increase insulin secretion?
No. They reduce hepatic glucose output and improve insulin action, which is why they rarely cause hypoglycemia when used alone.
Which organ function must be checked before and during biguanide treatment, and why?
Kidney function: metformin is excreted unchanged in urine, so a falling filtration rate lets it accumulate and raises the risk of lactic acidosis.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Metformin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.