What is the recommended oral iron supplementation regimen for patients with iron deficiency anemia?

Oral Iron Supplementation for Iron Deficiency Anemia

For adults with iron deficiency anemia, prescribe 50-100 mg of elemental iron once daily (or every other day for better tolerance), using ferrous sulfate as the least expensive option, and continue treatment for 3 months after hemoglobin normalizes to replenish iron stores. 1, 2

Dosing Regimen

Standard Daily Dosing

• Prescribe 50-100 mg elemental iron once daily as the standard approach for all adults (not weight-based) 2
• Ferrous sulfate is preferred as the least expensive formulation with no proven advantage of other preparations 1
• Common preparations and their elemental iron content:
  • Ferrous sulfate 200 mg = 65 mg elemental iron 2
  • Ferrous fumarate 322 mg = 106 mg elemental iron 2
  • Ferrous gluconate 324 mg = 38 mg elemental iron 3

Alternative Dosing for Better Tolerance

• Every-other-day dosing (60-120 mg elemental iron) may improve tolerability with similar or equal iron absorption compared to daily dosing 1, 4
• Give iron in the morning as a single dose rather than divided doses throughout the day, since afternoon/evening doses after a morning dose reduce absorption due to hepcidin elevation 4
• Lower doses (50-60 mg) should be used if gastrointestinal side effects occur 5

Enhancing Absorption

• Add vitamin C (ascorbic acid) to oral iron supplementation to improve absorption 1, 4
• Avoid taking iron with food or using enteric-coated formulations, as these decrease absorption despite improving tolerability 1

Treatment Duration and Monitoring

Initial Response Assessment

• Monitor hemoglobin within 4 weeks of starting therapy 1, 2
• Expect hemoglobin increase of at least 10 g/L after 2 weeks; absence of this rise predicts treatment failure (sensitivity 90.1%, specificity 79.3%) 2
• If no response after 4 weeks despite compliance and absence of acute illness, evaluate for malabsorption, ongoing blood loss, or consider alternative diagnoses 1

Continuation and Store Repletion

• Continue oral iron for 3 months after hemoglobin normalizes to replenish iron stores 2, 5, 6
• For confirmed iron-deficiency anemia in women, continue treatment for 2-3 additional months after correction 1
• Monitor blood counts every 4 weeks until hemoglobin normalizes, then periodically (every 6 months initially) to detect recurrence 2

When to Use Intravenous Iron Instead

Switch to intravenous iron if: 1, 2

• The patient does not tolerate oral iron despite dosing adjustments
• Ferritin levels do not improve with an adequate trial of oral iron
• Malabsorption is present (celiac disease, inflammatory bowel disease, post-bariatric surgery, post-gastric resection) 1
• Blood loss exceeds the ability to replete iron orally 1
• The patient has chronic inflammatory conditions where oral absorption is impaired 1, 2

Intravenous formulations requiring only 1-2 infusions are preferred over those requiring multiple infusions 1

Special Population Considerations

Pregnant Women

• Start low-dose oral iron (30 mg/day elemental iron) at the first prenatal visit for primary prevention 1
• For treatment of anemia during pregnancy, increase to 60-120 mg/day elemental iron 1
• Once hemoglobin normalizes for gestational age, decrease back to 30 mg/day 1

Inflammatory Bowel Disease

• Limit oral iron to no more than 100 mg elemental iron daily 1
• Consider intravenous iron for moderate to severe anemia (Hb <100 g/L) or oral intolerance 1
• Monitor for recurrent iron deficiency every 3 months for at least one year after correction 1

Post-Bariatric Surgery

• Intravenous iron is preferred for patients after bariatric procedures that disrupt duodenal absorption 1

Common Pitfalls to Avoid

• Do not switch between different traditional ferrous salts when side effects occur—this is not evidence-based; instead, reduce dose or switch to alternate-day dosing 2, 7
• Do not use modified-release or enteric-coated preparations—these have reduced absorption 2
• Do not stop treatment when hemoglobin normalizes—continue for 3 months to replenish stores 2, 5
• Do not prescribe doses higher than 100-120 mg daily—fractional absorption decreases with higher doses, increasing side effects without benefit 4
• Do not give divided doses throughout the day—single morning doses maximize absorption 4