What is the recommended dose of oral iron (ferrous sulfate) for a patient with iron deficiency anemia?

Recommended Oral Iron Dosing for Iron Deficiency Anemia

For most patients with iron deficiency anemia, prescribe 50-100 mg of elemental iron once daily, which can be achieved with a single tablet of ferrous sulfate 200 mg (containing 65 mg elemental iron) taken on an empty stomach. 1, 2

Standard Dosing Regimen

• Once-daily dosing of 50-100 mg elemental iron is superior to multiple daily doses because serum hepcidin levels remain elevated for up to 48 hours after iron intake, blocking further absorption and increasing side effects without improving efficacy 1

• The most cost-effective formulation is ferrous sulfate 200 mg tablets (providing 65 mg elemental iron), costing approximately £1.00 for a 28-day supply 1

• Iron should be taken on an empty stomach (1-2 hours before or after meals) to maximize absorption, though this may increase gastrointestinal side effects 1, 2

Special Consideration for Inflammatory Bowel Disease

In patients with active IBD, oral iron tablets should NOT be used, as systemic inflammation inhibits iron absorption. 3

• For patients with inactive IBD only, limit elemental iron to no more than 100 mg daily 3

• Consider parenteral iron for IBD patients with active disease or malabsorption 3, 1

Treatment Duration and Monitoring

• Continue treatment for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of iron stores 1, 2

• Monitor hemoglobin response within 2-4 weeks of starting treatment; expect an increase of approximately 1 g/dL within 2 weeks in responding patients 1, 2

• Absence of hemoglobin rise of at least 10 g/L after 2 weeks strongly predicts treatment failure (sensitivity 90.1%, specificity 79.3%) and warrants reassessment 1

Strategies to Improve Tolerability

If standard dosing causes intolerable side effects:

• Reduce to one tablet every other day (alternate-day dosing), which significantly increases fractional iron absorption compared to daily dosing due to hepcidin regulation 1

• Take iron with 250-500 mg vitamin C to enhance absorption through chelate formation 1

• Switch to alternative ferrous salts: ferrous fumarate (69-106 mg elemental iron per tablet) or ferrous gluconate (37 mg elemental iron per tablet) 1, 2

What to Avoid

• Do not prescribe multiple daily doses - this increases side effects without improving absorption due to hepcidin-mediated blockade 1

• Avoid modified-release preparations, which are less suitable for prescribing and more expensive 1, 2

• Do not take iron with tea, coffee, or calcium-containing foods/medications, which significantly inhibit absorption 1

• Avoid multivitamin preparations as sole iron source, as they contain insufficient elemental iron (typically ≤14 mg) for treating iron deficiency anemia 1

When to Consider Parenteral Iron

Switch to intravenous iron when:

• Oral iron is not tolerated despite dose modifications 1, 2
• Ferritin levels fail to improve after adequate oral iron trial 1
• Patient has conditions impairing oral iron absorption (active IBD, post-bariatric surgery, celiac disease) 3, 1
• Parenteral iron can produce clinically meaningful hemoglobin response within one week 1

Common Pitfalls

• Taking iron with food reduces absorption by up to 50% - counsel patients to take on empty stomach despite increased GI symptoms 2

• In IBD patients, ferritin levels up to 100 μg/L in the presence of inflammation may still reflect iron deficiency; measure transferrin saturation to confirm iron status 3

• Failure to respond may indicate non-compliance, continued blood loss, malabsorption, or concurrent vitamin B12/folate deficiency requiring evaluation 2