Metformin is the Primary Example of a Biguanide Medication
Metformin (metformin hydrochloride) is the most widely used and, in most of the world, the only biguanide medication currently available for clinical use 1, 2, 3.
The Biguanide Class
Biguanides are a class of antidiabetic medications characterized by two guanidine moieties fused together. While historically this class included several agents, metformin has emerged as the predominant—and in many countries, the sole—representative of this drug class in clinical practice 1.
Historical Context
Other biguanides that have existed include:
- Phenformin - discontinued in the United States in 1976 due to association with lactic acidosis 4
- Buformin - also discontinued due to safety concerns 4
- Proguanil - used for malaria prevention rather than diabetes 5
Mechanism of Action
Metformin's primary pharmacological effect is reducing hepatic glucose output and improving peripheral insulin resistance 3. It predominantly works by decreasing hepatic glucose production, which lowers fasting glycemia 2, 1.
Clinical Efficacy
Metformin typically lowers HbA1c by:
- 1.0% to 1.5% in clinical trials 1, 3
- Demonstrates weight stability or modest weight loss, unlike many other glucose-lowering medications 1
- Does not cause hypoglycemia when used as monotherapy 1
First-Line Status
Metformin is recommended as the most widely used first-line type 2 diabetes drug 2. Treatment guidelines from multiple countries and international organizations recommend metformin as the basic medication among first-line options for hyperglycemia control in type 2 diabetes 3.
Important Safety Considerations
Contraindications for Biguanides:
- Renal insufficiency (eGFR < 45 mL/min/1.73 m²) 3
- Liver dysfunction 3
- Severe infection or hypoxia 3
- Patients undergoing major surgery 3
Key Caveat
The dose should be reduced if eGFR is 45-59 mL/min/1.73 m², and metformin should be temporarily discontinued for patients undergoing angiography with iodinated contrast agents 3.