Metformin: Uses, Dosage, Side Effects, and More
1. Drug Name
Generic Name: Metformin
Brand Name(s):
- Pakistan: Glucophage
- India: Glycomet, Glyciphage
- United States: Glucophage, Fortamet, Glumetza, Riomet
- United Kingdom: Glucophage
2. Pharmacological Class
Class: Biguanide
Subclass: Antidiabetic agent
3. Mechanism of Action
Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.
4. Indications
Primary Indications:
- Type 2 diabetes mellitus
Off-label Uses:
- Polycystic ovary syndrome (PCOS)
- Weight loss in patients without diabetes
- Gestational diabetes (under medical supervision)
5. Dosage and Administration
Standard Dosage:
- Adults: Start with 500 mg twice daily or 850 mg once daily with meals, gradually increasing in increments of 500 mg weekly or 850 mg every two weeks, up to 2000-2550 mg daily in divided doses.
- Children (10 years and older): Usually 500 mg twice daily with meals, up to 2000-2550 mg daily in divided doses.
Route of Administration: Oral (tablets, extended-release tablets, oral solution).
Special Populations:
- Pediatric: Safety and efficacy not established in children under 10 years of age.
- Geriatric: Use with caution, as renal function declines with age; adjust dosage based on renal function.
6. Pharmacokinetics
Absorption: Rapidly and completely absorbed from the gastrointestinal tract.
Distribution: Distributed in tissues and fluids, with negligible binding to plasma proteins.
Metabolism: Not metabolized.
Excretion: Excreted unchanged in urine.
Half-life: Approximately 6.2 hours.
7. Contraindications
Metformin is contraindicated in patients with severe renal impairment (eGFR less than 30 mL/min/1.73 m²), acute or chronic metabolic acidosis, and in patients with a history of hypersensitivity to metformin.
8. Warnings and Precautions
Use with caution in patients with mild to moderate renal impairment (eGFR 30-60 mL/min/1.73 m²), as metformin accumulation may increase the risk of lactic acidosis.
Avoid in patients with conditions that predispose to lactic acidosis (e.g., sepsis, dehydration, shock).
9. Side Effects
Common Side Effects: Gastrointestinal disturbances (e.g., diarrhea, nausea, vomiting), metallic taste, vitamin B12 deficiency.
Serious Side Effects: Lactic acidosis (rare but serious complication), which can be fatal if not recognized and treated promptly. Discontinue metformin and seek medical attention if symptoms of lactic acidosis occur (e.g., malaise, myalgia, respiratory distress).
10. Drug Interactions
Major Interactions: Cimetidine, furosemide, and other drugs that are excreted via the renal tubular secretion pathway may interact with metformin, potentially leading to elevated levels of metformin and an increased risk of lactic acidosis.
Moderate Interactions: Alcohol, corticosteroids, diuretics, and beta-2 agonists.
Minor Interactions: Antidiabetic agents, such as insulin and sulfonylureas.
11. Pregnancy and Lactation
Pregnancy Category: Category B - Metformin is generally considered safe to use during pregnancy, although insulin is often preferred for controlling blood glucose levels.
Breastfeeding Considerations: Metformin is excreted into breast milk; use with caution while breastfeeding.
12. Patient Counseling Information
Key Points for Patients:
- Take metformin exactly as prescribed by your healthcare provider.
- Take with meals to reduce gastrointestinal side effects.
- Avoid excessive alcohol consumption while taking metformin.
Administration Tips:
- Swallow extended-release tablets whole; do not crush, chew, or break them.
- If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule.
- Monitor your blood glucose levels regularly as directed by your healthcare provider.