Metformin (Metformin Hydrochloride)

Metformin is indicated for conditions affecting glucose metabolism, primarily within the type 2 diabetes therapeutic pathway.

• Type 2 diabetes mellitus: improves glycemic control by lowering fasting and post‑prandial blood glucose.
• Prediabetes (impaired fasting glucose or impaired glucose tolerance): delays progression to overt diabetes when combined with lifestyle modification.
• Polycystic ovary syndrome (adjunct therapy): helps reduce insulin resistance and may improve menstrual regularity.

• Metformin acts primarily by inhibiting mitochondrial respiratory‑chain complex I, which decreases hepatic gluconeogenesis. It also reduces intestinal glucose absorption and enhances insulin‑mediated glucose uptake in peripheral tissues such as muscle. The drug also modulates AMP‑activated protein kinase (AMPK) activity, contributing to its metabolic effects. Additionally, metformin may improve lipid profiles and has modest effects on body weight.

Metformin may cause a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Gastrointestinal upset: nausea, abdominal discomfort, or diarrhea.
• Metallic taste: transient alteration in taste perception.
• Decreased vitamin B12 levels: may develop with long‑term therapy.
• Weight loss: modest reduction in body weight.

Serious or Rare Side Effects

• Lactic acidosis: rare but potentially fatal metabolic acidosis.
• Severe hypoglycemia: usually when combined with insulin or sulfonylureas.
• Hepatotoxicity: rare liver injury presenting with elevated enzymes.

When prescribing Metformin, clinicians should consider several precautionary measures to ensure patient safety.

• Renal function: assess creatinine clearance before initiation and periodically during therapy.
• Hepatic impairment: avoid use in patients with significant liver disease due to lactic acidosis risk.
• Contrast imaging: discontinue metformin before iodinated contrast procedures and restart after renal function is confirmed.
• Elderly patients: start at lower doses and monitor for accumulation.
• Concomitant alcohol: advise patients to limit alcohol intake to reduce lactic acidosis risk.
• Store at ambient temperature: keep below 25 °C in the original container, protected from moisture and light.

Metformin’s pharmacokinetic profile leads to several clinically relevant drug interactions.

Major Interactions (Avoid)

• Iodinated contrast agents: may precipitate acute renal failure and increase lactic acidosis risk; discontinue metformin before and after the procedure.
• Cimetidine: can increase metformin plasma concentrations, raising the risk of toxicity.
• Nitrates (e.g., nitroglycerin): may potentiate hypotensive effects when combined with metformin‑induced vasodilation.

Moderate Interactions (Monitor Closely)

• ACE inhibitors or ARBs: monitor renal function as combined effect may impair clearance.
• Diuretics (especially thiazides): may affect electrolyte balance and renal function.
• Beta‑blockers: may mask hypoglycemia symptoms when metformin is used with insulin secretagogues.
• Oral corticosteroids: can increase blood glucose, requiring dose adjustments.