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Metformin

Metformin, a cornerstone in the management of type 2 diabetes mellitus (T2DM), is renowned for its efficacy, safety, and pleiotropic benefits. This article synthesizes evidence from the British National Formulary (BNF), Lippincott Textbook of Pharmacology, and Lange Basic & Clinical Pharmacology to provide a detailed overview of its mechanism of action, clinical uses, dosing, side effects, precautions, and drug interactions

Metformin, a biguanide, exerts its antihyperglycemic effects through multiple pathways:

Hepatic Gluconeogenesis Inhibition

Activates AMP-activated protein kinase (AMPK), a cellular energy sensor, reducing hepatic glucose production (Lippincott).

 

Suppresses mitochondrial glycerophosphate dehydrogenase, altering redox potential and inhibiting gluconeogenesis (Lange).

Peripheral Insulin Sensitivity:

Enhances glucose uptake in skeletal muscle and adipose tissue by improving insulin receptor tyrosine kinase activity (Lange).

Gastrointestinal Effects:

Modulates gut microbiota, increasing glucagon-like peptide-1 (GLP-1) secretion, which suppresses appetite and improves glucose regulation (emerging research noted in Lippincott).

Primary Indication:

Type 2 Diabetes Mellitus: First-line therapy, particularly for overweight patients (BNF). Often combined with lifestyle modifications or other agents (e.g., sulfonylureas, SGLT2 inhibitors).

Off-Label Uses:

Polycystic Ovary Syndrome (PCOS): Improves insulin resistance and regulates menstrual cycles (Lange).

Prediabetes: Reduces progression to T2DM (Lippincott).

Initial Dose: 500 mg once daily (with meals) to minimize gastrointestinal (GI) effects (BNF).

Maintenance: Titrate weekly by 500 mg, up to 2,000–3,000 mg/day in divided doses.

Extended-Release (XR): 500–2,000 mg once daily (BNF).

Renal Adjustment:

Avoid if eGFR <30 mL/min/1.73m².

Use with caution if eGFR 30–45 mL/min/1.73m² (BNF).

Common:

GI disturbances (30% of patients): Nausea, diarrhea, abdominal pain (Lippincott).

Rare but Serious:

Lactic Acidosis: Risk factors include renal/hepatic impairment, alcoholism, and acute hypoxia (BNF).

Vitamin B12 Deficiency: Long-term use may impair absorption; monitor levels annually (Lange).

Contraindications:

Severe renal impairment (eGFR <30), metabolic acidosis, acute dehydration (BNF).

Elderly: Higher risk of renal dysfunction; monitor eGFR regularly.

Pregnancy: Category not recommended; use only if benefits outweigh risks (BNF).

Cimetidine: Competes for renal tubular secretion, increasing metformin levels (BNF).

Alcohol: Potentiates lactate production; avoid excessive intake (Lange).

Loop Diuretics: May worsen renal function, increasing lactic acidosis risk (Lippincott).

Insulin/Sulfonylureas: Enhanced hypoglycemia risk when combined (BNF).

Generic: Metformin hydrochloride.

Brand Names: Glucophage®, Glumetza®, Fortamet®, Riomet® (liquid formulation).

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