Biguanides (Metformin)

Question 1

What is the method of action of metformin?

Answer 1

• ↑ sensitivity to insulin
• Method not completely understood
• ↓ hepatic glucose production
• ↑ glucose uptake and utilisation by skeletal muscle
• ↓ intestinal glucose absorption
• Induces weight loss

Question 2

What are the indication for metformin?

Answer 2

• Type 2 diabetes – 1st choice alone or in combination with other drugs

Question 3

What are the contraindications of metformin?

Answer 3

• Severe renal impairment
• Moderate renal impairment – dose reduction
• AKI – withhold acutely
• Severe tissue hypoxia
• Hepatic impairment – caution as clearance of excess lactate may be impaired
• Acute alcohol intoxication – withhold acutely due to lactic acidosis risk
• Chronic alcohol overuse – risk of hypoglycaemia

Question 4

What are the side effects of metformin?

Answer 4

• GI upset
• Weight loss
• Lactic acidosis – rare but fatal

Question 5

What drugs interact with metformin?

Answer 5

• IV contrast media – withhold before and for 48 hours after injection as risk of renal impairment, metformin accumulation and lactic acidosis
• ACE inhibitors – impair renal function
• NSAIDs – impair renal function
• Diuretics – impairs renal function
• Drugs the elevate blood glucose e.g. prednisolone, thiazide, loop diuretics

Question 6

What organ eliminates metformin?

Answer 6

Kidney

Question 7

What information should be given to a patient taking metformin?

Answer 7

• Take with or after food
• Lifestyle measures advice
• Explain signs of lactic acidosis and hypoglycaemia
• Tell a doctor you are on metformin before having an x-ray/operation