Oral Iron Dosing for Iron Deficiency Anemia
The recommended oral iron dose for adults with IDA is 50-100 mg of elemental iron once daily, taken on an empty stomach, regardless of the hemoglobin or hematocrit level—dosing is not weight-based or titrated to specific hemoglobin values. 1, 2
Standard Dosing Approach
The key principle is that oral iron dosing does not vary based on hemoglobin or hematocrit levels—all adults with IDA receive the same initial dose. 1, 2
Initial Treatment
- Start with 50-100 mg elemental iron once daily (e.g., one ferrous sulfate 200 mg tablet = 65 mg elemental iron) 1, 2
- Take in the fasting state to maximize absorption 1
- This single daily dose represents the optimal balance between efficacy and tolerability 1
Common Oral Iron Preparations
- Ferrous sulfate 200 mg = 65 mg elemental iron 2
- Ferrous fumarate 322 mg = 106 mg elemental iron 2
- Ferrous gluconate 300 mg = 37 mg elemental iron 2
Monitoring Response (Not Dosing Adjustment)
While hemoglobin levels guide treatment success, they do not determine the oral iron dose:
- Check hemoglobin at 2 weeks: Absence of ≥10 g/L rise predicts treatment failure with 90% sensitivity 1, 2
- Monitor every 4 weeks until hemoglobin normalizes 1, 2
- If inadequate response at 2 weeks, consider increasing to twice daily dosing OR switching to alternate-day dosing if side effects are the issue 1
Special Population: IBD Patients
The only exception where hemoglobin influences the treatment route (not oral dose):
- Hemoglobin 11.0-12.9 g/dL (men) or 11.0-11.9 g/dL (women): Oral iron acceptable if disease inactive 1
- Hemoglobin <10 g/dL: Consider intravenous iron as first-line instead 1
- Maximum 100 mg elemental iron daily in IBD patients (lower than general population) 1
When Oral Iron Fails or Is Inappropriate
Switch to intravenous iron (not higher oral doses) when: 1, 2
- No hemoglobin rise ≥10 g/L after 2 weeks of daily oral therapy 1
- Severe anemia with hemoglobin <7 g/dL 1
- Gastrointestinal intolerance to oral preparations 1
- Malabsorption conditions (celiac disease, post-bariatric surgery) 1, 3
- Active inflammatory bowel disease 1
- Chronic kidney disease or heart failure 1, 3
Treatment Duration
- Continue oral iron for 3 months after hemoglobin normalization to replenish iron stores 1, 2
- The duration is fixed, not adjusted based on initial hemoglobin level 1
Critical Pitfalls to Avoid
- Do not prescribe higher oral doses based on lower hemoglobin levels—this only increases side effects without improving absorption 1
- Do not switch between different iron salts (ferrous sulfate to ferrous fumarate) for side effects—this lacks evidence 1, 2
- Avoid modified-release preparations—they have reduced absorption and are less suitable 1
- Do not stop treatment when hemoglobin normalizes—stores require additional 3 months of therapy 1, 2