Oral Iron Dosing for Iron Deficiency Anemia
For a 43-year-old female with hemoglobin 8.6 g/dL, prescribe ferrous sulfate 200 mg (65 mg elemental iron) once daily in the morning on an empty stomach, together with 250–500 mg vitamin C, and expect hemoglobin to rise by at least 1 g/dL within 2 weeks if treatment is effective. 1, 2
First-Line Oral Iron Regimen
Ferrous sulfate 200 mg (65 mg elemental iron) taken once daily in the morning on an empty stomach is the gold-standard, most cost-effective formulation (approximately £1.00 per 28-day supply versus £47.60 for alternatives). 1, 2
Single morning dosing is superior to multiple daily doses because elemental iron ≥60 mg triggers a hepcidin surge lasting 24–48 hours that blocks absorption of subsequent doses by 35–45%, while increasing gastrointestinal side effects without improving hemoglobin response. 1, 2, 3
Co-administer 250–500 mg vitamin C with each iron dose to form a soluble chelate and enhance absorption, especially important when transferrin saturation is low. 1, 2
Take iron 1–2 hours before or after meals to maximize absorption by up to 50%, though taking with a small amount of food is acceptable if gastrointestinal intolerance occurs. 1, 2
Expected Response and Monitoring Timeline
Check hemoglobin at 2 weeks; a rise of ≥10 g/L (≥1 g/dL) predicts treatment success with 90% sensitivity and 79% specificity. 1, 2
Failure to achieve this ≥10 g/L rise at 2 weeks strongly predicts overall treatment failure and warrants evaluation for non-adherence, ongoing blood loss, malabsorption, or concurrent vitamin B12/folate deficiency. 1, 2
Monitor hemoglobin every 4 weeks until normalization, then continue oral iron for an additional 3 months to fully replenish iron stores, resulting in a total treatment duration of approximately 6–7 months. 1, 2
Alternative Dosing Strategy for Intolerance
If daily dosing causes intolerable gastrointestinal side effects, switch to alternate-day (every-other-day) dosing with 100–200 mg elemental iron, which markedly increases fractional iron absorption, reduces side effects, and maintains overall efficacy, though the early rate of hemoglobin rise may be slower. 1, 2, 3, 4
Alternate-day dosing works because hepcidin elevation subsides by 48 hours, allowing improved absorption when iron is given every other day rather than consecutively. 3
Critical Pitfalls to Avoid
Do not prescribe multiple daily doses; hepcidin-mediated blockade prevents absorption of second and third doses while increasing gastrointestinal adverse effects. 1, 2, 3
Do not take iron with tea, coffee, or calcium-containing foods/supplements within 1–2 hours, as these markedly reduce absorption. 1, 2
Do not discontinue iron when hemoglobin normalizes; continue therapy for an additional 3 months to restore iron stores. 1, 2
Do not switch between different ferrous salts (ferrous sulfate, ferrous fumarate, ferrous gluconate) expecting better tolerability, as evidence does not support this practice. 1, 2
Do not use modified-release iron preparations, as they release iron beyond the duodenum (the primary absorption site) and are classified as "less suitable for prescribing" by the British National Formulary. 1, 2
When to Escalate to Intravenous Iron
Consider intravenous iron if any of the following occur:
Ferritin fails to improve after 4 weeks of compliant oral therapy despite adequate dosing and vitamin C supplementation. 1, 2
Transferrin saturation remains <20% after an adequate oral trial. 2
Intolerance to ≥2 different oral iron preparations. 2
Active inflammatory bowel disease with hemoglobin <10 g/dL, where inflammation-induced hepcidin elevation impairs oral iron absorption and oral iron may exacerbate intestinal inflammation. 1, 2
Post-bariatric surgery patients, in whom duodenal iron absorption is anatomically disrupted. 1, 2
Celiac disease with inadequate response to oral iron despite strict adherence to a gluten-free diet. 1, 2
Intravenous Iron Formulations
Prefer high-dose formulations that replenish the iron deficit in 1–2 infusions (ferric carboxymaltose 750–1000 mg per 15-minute infusion, or ferric derisomaltose 1000 mg single infusion) to minimize clinic visits. 1, 2
For a 70-kg female with hemoglobin 8.6 g/dL, the calculated total elemental iron deficit is approximately 1,500 mg, which can be repleted in 1–2 infusions with modern formulations. 2
Intravenous iron produces a clinically meaningful hemoglobin rise within 1 week and should be considered an alternative to blood transfusion in most cases. 1, 2
All approved intravenous iron products have comparable safety; true anaphylaxis is exceedingly rare (<1%), and most adverse reactions are complement-activation-related pseudo-allergic infusion reactions that respond to antihistamines and corticosteroids rather than epinephrine. 2