💊 Metformin
Drug Class & Overview
Metformin is a biguanide, an oral antihyperglycaemic agent and the first-line pharmacological treatment for Type 2 Diabetes Mellitus, particularly in overweight or obese patients.
Mechanism of Action
Metformin primarily reduces hepatic glucose production by inhibiting gluconeogenesis. It also improves insulin sensitivity in peripheral tissues (muscle and adipose tissue) and decreases intestinal glucose absorption. It does not stimulate insulin secretion.
Key Indications
Metformin is the first-line drug for Type 2 Diabetes Mellitus, especially in those who are overweight or obese. It can be used as monotherapy or in combination with other oral antidiabetic agents or insulin. It is also used in Polycystic Ovary Syndrome (PCOS) to improve insulin sensitivity.
Contraindications
Absolute contraindications include severe renal impairment (eGFR <30 mL/min/1.73m²), metabolic acidosis (including diabetic ketoacidosis), and severe hepatic impairment. It should be temporarily withheld in conditions that may cause acute renal impairment or hypoxia, such as acute heart failure, sepsis, or before/during procedures involving iodinated contrast media.
Adverse Effects
Common adverse effects include gastrointestinal disturbances such as nausea, vomiting, diarrhoea, and abdominal pain, which can often be mitigated by slow dose titration and taking with food. A rare but serious adverse effect is lactic acidosis, particularly in patients with renal impairment or acute illness.
Monitoring
Renal function (eGFR) should be checked before initiating metformin and at least annually thereafter, or more frequently in patients at risk of renal impairment. Vitamin B12 levels should be considered in patients on long-term metformin therapy, especially if anaemia or neuropathy develops.
Prescribing Safety (OSCE)
Always check renal function before prescribing metformin and ensure it is not severely impaired. Counsel patients on common GI side effects and the importance of taking it with food. Advise patients to temporarily stop metformin if they become acutely unwell, dehydrated, or are undergoing procedures with contrast media.
MLA High-Yield Notes
Metformin is the cornerstone of Type 2 Diabetes management. Its key advantage is that it does not cause hypoglycaemia when used as monotherapy. Remember the risk of lactic acidosis in renal impairment and the need for temporary cessation in acute illness. Consider Vitamin B12 deficiency with long-term use.
Common SBA Themes
SBAs frequently test the contraindications of metformin, particularly renal impairment and the risk of lactic acidosis. Questions may also focus on its role as first-line therapy in Type 2 Diabetes and its mechanism of action without causing hypoglycaemia.
References
- BNF (British National Formulary)
- NICE Guideline NG28: Type 2 diabetes in adults: management
- MHRA Drug Safety Update: Metformin and risk of lactic acidosis