Metformin
Metformin
Generic Name
Metformin
Mechanism
Decreases hepatic gluconeogenesis, improves insulin‑mediated glucose uptake in peripheral tissues (primarily skeletal muscle), and modestly inhibits intestinal glucose absorption.
Pharmacokinetics
- Oral absorption: ~50 % bioavailability; peak plasma 1–2 h.
- Renally eliminated unchanged; half‑life ≈ 4–8 h (longer in CKD).
- No hepatic metabolism → no active metabolites.
Clinical Pearls
- Cimetidine, diuretics (e.g., furosemide), and ions (Na⁺, K⁺, Ca²⁺, Mg²⁺) → ↑ plasma metformin.
- Contrast agents (especially iodinated) → ↑ risk of lactic acidosis.
- Alcohol or drugs that decrease renal perfusion (ACEi, ARB, NSAIDs) → ↑ metformin levels.
Clinical Notes
Metformin (generic) – biguanide antihyperglycemic agent
| Category | Key Points |
|---|---|
| Indication | Type 2 diabetes mellitus (alone or in combination with diet, exercise, or other oral agents). Used adjunctively with insulin or for pre‑diabetes. |
| Mechanism of Action | Decreases hepatic gluconeogenesis, improves insulin‑mediated glucose uptake in peripheral tissues (primarily skeletal muscle), and modestly inhibits intestinal glucose absorption. |
| Pharmacokinetics | • Oral absorption: ~50 % bioavailability; peak plasma 1–2 h. • Renally eliminated unchanged; half‑life ≈ 4–8 h (longer in CKD). • No hepatic metabolism → no active metabolites. |
| Dosing (adult) | • Initiate 500 mg PO BID or 850 mg QHS with meals (to reduce GI upset). • Titrate by 500 mg increments every 1–2 weeks to a maximum of 2000–2550 mg/day in divided doses. • Initiate at lower doses in CKD or elderly. |
| Key Contraindications | • Renal impairment (CrCl < 30 mL/min). • Severe hepatic disease. • Metabolic acidosis (including diabetic ketoacidosis). • Conditions that predispose to hypoxia (pulmonary disease, severe CHF, recent MI). |
| Common Adverse Effects | • GI disturbance (nausea, vomiting, diarrhea, abdominal discomfort). • Rare: lactic acidosis (1–2 cases/100 000 per year). |
| Drug Interactions | • Cimetidine, diuretics (e.g., furosemide), and ions (Na⁺, K⁺, Ca²⁺, Mg²⁺) → ↑ plasma metformin. • Contrast agents (especially iodinated) → ↑ risk of lactic acidosis. • Alcohol or drugs that decrease renal perfusion (ACEi, ARB, NSAIDs) → ↑ metformin levels. |
| Renal Function Monitoring | • Baseline CrCl before initiation. • Re‑evaluate when CrCl 30–60 mL/min, then every 3–6 months. |
| Other Considerations | • No weight gain; may cause modest weight loss. • No significant interaction with insulin actions → can be used for dose‑sparing. • Use caution in pregnancy (category B). |
| Reference | ADA Standards of Care 2024; NICE Guideline NG28 (Type 2 Diabetes); WHO Model List of Essential Medicines. |
Quick‐reference tip: Start low, go slow, titrate on meals, avoid in impaired kidneys or conditions that can precipitate lactic acidosis.
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