Iron Supplement Dosing for Iron Deficiency Anemia
Recommended Initial Dosing
For adults with iron deficiency anemia, start with 50-100 mg of elemental iron once daily, taken in the fasting state, as this represents the optimal balance between efficacy and tolerability. 1, 2
Specific Oral Iron Preparations
The most commonly used oral iron formulations and their elemental iron content are:
- Ferrous sulfate 200-325 mg tablet = 65 mg elemental iron (one tablet daily) 1, 2, 3
- Ferrous fumarate 325 mg tablet = 106 mg elemental iron (one tablet daily) 1, 2
- Ferrous gluconate 325 mg tablet = 38 mg elemental iron (3-4 tablets daily to reach target dose) 1, 4
- Ferric maltol 30 mg = 30 mg elemental iron (one tablet twice daily) 1
Timing and Administration Strategy
Take iron on an empty stomach (fasting state) to maximize absorption, as food significantly reduces iron bioavailability. 1
If gastrointestinal side effects occur, consider alternate-day dosing (60-120 mg every other day) rather than switching to a different iron salt, as this approach may improve both absorption and tolerability. 1, 5 The British Society of Gastroenterology guidelines note that alternate-day dosing produces similar hemoglobin increments after the same total dose with significantly lower nausea rates. 1
Administer iron doses in the morning only, not in divided doses throughout the day. 5 Recent evidence shows that oral iron doses ≥60 mg stimulate hepcidin elevation that persists for 24 hours, which blocks subsequent iron absorption if additional doses are given the same day. 5
Monitoring Response
Check hemoglobin after 2 weeks of treatment—failure to achieve at least a 10 g/L rise predicts treatment failure with 90% sensitivity and 79% specificity. 1, 2
Monitor hemoglobin every 4 weeks until normalization is achieved. 1, 2
Treatment Duration
Continue oral iron for 3 months after hemoglobin normalizes to replenish iron stores. 1, 2 While traditionally 2-3 months has been recommended, the exact duration needed for complete store repletion remains unclear. 1
After treatment completion, monitor blood counts every 3 months for the first year, then every 6 months for 2-3 years to detect recurrent anemia. 1, 2
When to Switch to Parenteral Iron
Consider intravenous iron in the following situations:
- Failure to respond to oral iron after 2 weeks (no 10 g/L hemoglobin rise) 1, 2
- Significant gastrointestinal intolerance despite alternate-day dosing 1, 2
- Chronic inflammatory conditions or ongoing blood loss 1, 2
- Documented malabsorption (celiac disease, inflammatory bowel disease, post-bariatric surgery) 1
For intravenous iron in non-CKD patients, ferric carboxymaltose and ferric derisomaltose allow single high-dose infusions (up to 1000 mg or 20 mg/kg) with 15-30 minute infusion times. 1
Special Population: CKD Patients
For patients with chronic kidney disease and iron deficiency anemia, higher oral doses are recommended:
- Ferrous sulfate: 1000 mg/day (approximately 325 mg elemental iron) 1
- Ferrous fumarate: 600 mg/day (approximately 200 mg elemental iron) 1
- Ferric citrate: 210 mg elemental iron three times daily with meals 1
Critical Pitfalls to Avoid
Do not switch between different traditional ferrous salts (sulfate, fumarate, gluconate) when side effects occur—this practice is not evidence-based. 1 Instead, try alternate-day dosing, ferric maltol, or parenteral iron. 1
Avoid modified-release iron preparations, as they are less suitable for prescribing due to reduced absorption in the distal small bowel where iron uptake is minimal. 1
Do not use blood transfusion routinely for iron deficiency anemia—reserve it only for severe symptomatic anemia with circulatory compromise, targeting hemoglobin 70-90 g/L. 1, 2 Parenteral iron produces clinically meaningful hemoglobin response within one week and should be considered first. 1
Withhold intravenous iron during active infections, as these patients were excluded from randomized trials and iron may theoretically increase infection risk. 1