Metformin

Metformin

Drug monograph · NCLEX study reference
Trade names	Glucophage
Therapeutic class	Antidiabetic
Pharmacologic class	Biguanide
Onset / peak / duration	Onset within days; ER once daily; full glycemic effect over 1 to 2 weeks.
Half-life / level	Half-life about 6 hours; no routine level.
Routes	PO (oral)
High-alert (ISMP)	No
Black box warning	Yes (see Safety)
Antidote / reversal	None; supportive care and hemodialysis for severe lactic acidosis.
Pregnancy / lactation	Sometimes continued in pregnancy under specialist care.

Nursing pharmacology study reference (NCLEX-style monograph). Numeric values are standard teaching ranges for study and must be verified against current manufacturer labeling before clinical use. This is educational content, not prescribing guidance.

Metformin (brand name Glucophage) — Antidiabetic; Biguanide.

Identification

• Therapeutic class: Antidiabetic.
• Pharmacologic class: Biguanide.

Pharmacology

• Mechanism of action: Decreases hepatic glucose production, reduces intestinal glucose absorption, and improves insulin sensitivity; does not cause hypoglycemia alone.
• Onset / peak / duration: Onset within days; ER once daily; full glycemic effect over 1 to 2 weeks.
• Half-life / therapeutic level: Half-life about 6 hours; no routine level.

Clinical use

• Indications: Type 2 diabetes (first line), prediabetes, polycystic ovary syndrome (off-label).
• Usual dose, route, frequency: 500 to 1,000 mg PO twice daily, or ER once daily with the evening meal.
• Maximum dose / adjustments: Max about 2,550 mg/day (2,000 mg ER); dose by renal function (eGFR), do not start if eGFR below 45, stop if below 30; hold around iodinated contrast.

Safety

• Contraindications: eGFR below 30, metabolic acidosis, acute conditions risking renal hypoperfusion.
• Black box warning: Risk of lactic acidosis, especially with renal impairment, hypoxia, sepsis, or excess alcohol.
• Interactions: Iodinated contrast (hold), alcohol (food/drink, raises lactic acidosis risk), cimetidine, carbonic anhydrase inhibitors.
• Pregnancy / lactation: Sometimes continued in pregnancy under specialist care.
• High-alert: No.

Adverse effects

• Common side effects: Diarrhea, nausea, metallic taste, abdominal cramping, B12 deficiency with long use.
• Serious effects to report: Lactic acidosis (muscle pain, trouble breathing, unusual fatigue, cold feeling).
• Antidote / reversal: None; supportive care and hemodialysis for severe lactic acidosis.

Nursing process

• Assessment before administration: Renal function (eGFR), B12 status, hydration, alcohol use.
• Interventions during therapy: Hold before and after contrast studies; take with food.
• Monitor: A1c, fasting glucose, renal function, vitamin B12 periodically.
• Evaluation / expected outcome: A1c at goal without hypoglycemia.

Patient teaching

• Patient teaching: Take with meals; GI effects usually ease; limit alcohol.
• Notify provider if: Muscle pain, trouble breathing, unusual tiredness, severe GI upset.
• Administration tips: With food; swallow ER whole; the ghost shell in stool is normal.