What is the recommended oral iron dosage for iron deficiency anemia (IDA)?

Recommended Oral Iron Dosage for Iron Deficiency Anemia

For most adults with iron deficiency anemia, take 50-100 mg of elemental iron once daily in the morning on an empty stomach, using ferrous sulfate as the first-line formulation. 1

First-Line Iron Formulation

• Ferrous sulfate is the gold standard and most cost-effective option, with a standard 200 mg tablet (or 324 mg tablet) providing 65 mg of elemental iron 1, 2
• Ferrous sulfate costs approximately £1.00 for a 28-day supply, making it significantly less expensive than alternative formulations 1
• No single iron formulation has proven advantages over others in terms of tolerability according to the American College of Gastroenterology 1

Optimal Dosing Strategy

The British Society of Gastroenterology and American Gastroenterological Association recommend once-daily dosing of 50-100 mg elemental iron rather than multiple daily doses. 1 This recommendation is based on the physiological understanding that:

• Oral iron doses ≥60 mg stimulate hepcidin elevation that persists for 24 hours and blocks subsequent iron absorption 1
• Taking 60 mg elemental iron once daily produces similar overall absorption to 60 mg taken twice daily, with 35-45% reduction in absorption from the second dose 1
• Multiple daily doses increase gastrointestinal side effects without improving absorption 1

Timing and Administration

• Take iron in the morning on an empty stomach (1-2 hours before or after meals) to maximize absorption 1
• If standard doses are not tolerated, consider taking with 250-500 mg vitamin C to enhance absorption 1
• Avoid taking iron with tea, coffee, or calcium-containing foods/medications, which inhibit absorption 1

Alternative Dosing for Intolerance

If once-daily dosing causes intolerable side effects:

• Alternate-day dosing with 100-200 mg elemental iron leads to significantly increased fractional iron absorption compared to daily dosing, though the rate of hemoglobin rise may be slower initially 1, 3
• When serum hepcidin remains elevated for up to 48 hours after an iron dose, alternate-day dosing allows hepcidin to subside and improves absorption 1
• Consider reduced dose, taking with food, or switching to alternative ferrous salts (ferrous fumarate provides 69-106 mg elemental iron per tablet; ferrous gluconate provides 37-38 mg elemental iron per tablet) 1, 4

Expected Response and Monitoring

• Hemoglobin should rise by at least 10 g/L (approximately 1 g/dL) within 2 weeks of starting daily oral iron therapy 1, 5
• Failure to achieve this rise strongly predicts subsequent treatment failure with 90.1% sensitivity and 79.3% specificity 1, 5
• Monitor hemoglobin response within the first 4 weeks of treatment 1, 5

Duration of Therapy

• Continue oral iron for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of marrow iron stores 1, 5
• This extended treatment period is necessary to replenish iron stores, not just correct anemia 5
• After successful treatment, monitor blood counts periodically (initially every 6 months) to detect recurrent IDA 5

Special Populations

Chronic Kidney Disease

• The National Kidney Foundation recommends 200 mg of elemental iron per day in 2-3 divided doses for patients with chronic kidney disease 1

Pregnant Women

• The Centers for Disease Control and Prevention recommend 60-120 mg/day of elemental iron for treatment of anemia in pregnancy 1
• Low-dose (30 mg/day) supplements are recommended at the first prenatal visit for prevention 1

Common Pitfalls to Avoid

• Do not prescribe modified-release preparations, as they are less suitable for prescribing according to the British National Formulary 1
• Do not rely on multivitamin preparations, which typically contain insufficient elemental iron (up to 14 mg) for treating iron deficiency anemia 1
• Do not continue oral iron indefinitely without monitoring, as failure to respond may indicate non-compliance, malabsorption, continued bleeding, or concurrent vitamin B12/folate deficiency 1
• Switching between different ferrous salts (ferrous fumarate, ferrous gluconate) is not supported by evidence for improving tolerability 1

When to Consider Intravenous Iron

Consider parenteral iron when:

• Oral iron is not tolerated despite modifications 1, 5
• Ferritin levels do not improve with oral iron trial 1
• Patient has conditions where oral iron absorption is impaired (inflammatory bowel disease, post-bariatric surgery, celiac disease, atrophic gastritis) 1, 6
• Ongoing blood loss is present 5
• Rapid correction is needed (intravenous iron produces clinically meaningful hemoglobin response within one week) 1