What are the best iron supplements for treating iron deficiency anemia?

Best Iron Supplements for Anemia

Ferrous sulfate 200 mg once daily is the best iron supplement for treating iron deficiency anemia, as it is the most cost-effective and equally efficacious as all other oral iron formulations. 1

First-Line Oral Iron Treatment

• Start with ferrous sulfate 200 mg (containing 65 mg elemental iron) taken once daily 1, 2, 3
• Once-daily dosing is superior to multiple daily doses because it improves tolerance while maintaining equal or better iron absorption 1, 4
• No single oral iron formulation has any therapeutic advantage over another—the choice is purely economic 1

Alternative Oral Formulations (If Ferrous Sulfate Not Tolerated)

• Ferrous fumarate (106 mg elemental iron per 325 mg tablet) 1
• Ferrous gluconate (38 mg elemental iron per 325 mg tablet) 1
• These alternatives are equally effective but typically more expensive 1, 5

Optimizing Oral Iron Absorption

• Add vitamin C (ascorbic acid) 500 mg with each iron dose to enhance absorption 1, 2
• This is particularly critical when initial response is poor or iron saturation is severely low 2
• Take iron on an empty stomach for optimal absorption, though taking with food is acceptable if gastrointestinal side effects occur 2

Dosing Schedule for Maximum Effectiveness

• Give iron once daily at most—never multiple times per day 1
• Consider alternate-day dosing (every other day) for patients with side effects, as this may improve tolerance with similar absorption rates 1, 4
• Morning dosing is preferred over afternoon or evening administration 4
• The rationale: oral iron doses ≥60 mg stimulate hepcidin elevation that persists 24 hours, blocking subsequent iron absorption 4

When to Switch to Intravenous Iron

Intravenous iron should replace oral therapy in these specific situations: 1, 2

• Intolerance to at least two different oral iron preparations 1, 2
• Failure of ferritin levels to improve after 4 weeks of compliant oral therapy 1, 2
• Active inflammatory bowel disease with hemoglobin <10 g/dL 1, 2
• Post-bariatric surgery patients (disrupted duodenal absorption) 1, 2
• Celiac disease with inadequate response despite gluten-free diet adherence 2
• Ongoing gastrointestinal blood loss exceeding oral replacement capacity 2

Preferred IV Iron Formulations

• Choose IV iron preparations that replace iron deficits in 1-2 infusions rather than multiple infusions 1
• Ferric carboxymaltose (500-1000 mg single doses, delivered within 15 minutes) is preferred 2
• Avoid iron dextran preparations due to higher anaphylaxis risk requiring test doses 2
• True anaphylaxis to IV iron is very rare—most reactions are complement activation-related pseudo-allergy (infusion reactions) 1

Treatment Duration and Monitoring

• Continue oral iron therapy for 3 months after hemoglobin normalizes to fully replenish iron stores 1, 2
• Expect hemoglobin to rise by approximately 2 g/dL after 3-4 weeks of treatment 2
• Monitor hemoglobin and red cell indices every 3 months for the first year, then again after another year 1, 2

Common Pitfalls to Avoid

• Do not prescribe multiple daily doses—this increases side effects without improving efficacy and actually reduces absorption due to hepcidin elevation 1, 4
• Do not stop iron when hemoglobin normalizes—stores require 3 additional months to replenish 1, 2
• Do not continue ineffective oral iron beyond 4 weeks—reassess and switch to IV iron if no hemoglobin rise occurs 2
• Do not overlook vitamin C supplementation when oral iron response is suboptimal 1, 2
• Do not fail to identify and treat the underlying cause while supplementing iron 1, 2

Special Population Considerations

Pregnant Women

• Start with oral low-dose iron 30 mg/day at first prenatal visit for prevention 1
• Treat anemia with 60-120 mg/day elemental iron 1
• Refer for further evaluation if hemoglobin <9.0 g/dL 1

Inflammatory Bowel Disease

• IV iron is first-line treatment when hemoglobin <10 g/dL with active inflammation 1, 2
• Treat underlying inflammation first to enhance iron absorption 2

Post-Bariatric Surgery

• IV iron is strongly preferred due to disrupted duodenal absorption mechanisms 1, 2

Failure to Respond

If anemia persists after 4 weeks of compliant therapy: 2

• Assess for continued blood loss
• Evaluate for malabsorption syndromes (celiac disease, inflammatory bowel disease)
• Consider further gastrointestinal investigation
• Verify patient adherence
• Switch to IV iron if oral route is the problem