What oral elemental iron dose is appropriate for an adult with a hemoglobin of 8.9 g/dL?

Oral Iron Dosing for Hemoglobin 8.9 g/dL

For an adult with hemoglobin 8.9 g/dL, start with 50–100 mg elemental iron once daily in the morning on an empty stomach, using ferrous sulfate 200 mg tablets (providing 65 mg elemental iron per tablet). 1

First-Line Oral Iron Regimen

• Ferrous sulfate 200 mg (65 mg elemental iron) taken once daily in the morning, 1–2 hours before meals, is the gold-standard first-line treatment for iron deficiency anemia at this hemoglobin level 1, 2
• This single daily dose provides equivalent hemoglobin response to divided doses while causing fewer gastrointestinal side effects 1, 2
• Ferrous sulfate costs approximately £1.00 for a 28-day supply, making it the most cost-effective option 1, 2

Why Once-Daily Dosing Is Superior

• Oral iron doses ≥60 mg elemental iron trigger hepcidin elevation that persists for 24 hours, blocking absorption of subsequent doses by 35–45% 3, 2
• Multiple daily doses significantly increase gastrointestinal symptoms without improving hemoglobin response 2, 1
• The circadian increase in plasma hepcidin is augmented by a morning iron dose; therefore, iron should not be given in the afternoon or evening 3

Alternative Dosing if Standard Regimen Not Tolerated

• If daily dosing causes intolerable gastrointestinal side effects, switch to alternate-day dosing (every other day) with 100–200 mg elemental iron 1, 2, 3
• Alternate-day dosing markedly increases fractional iron absorption compared to daily dosing and reduces side effects while maintaining efficacy 1, 3
• This approach allows hepcidin levels to subside by 48 hours, optimizing absorption of the next dose 3

Enhancing Absorption

• Co-administer 250–500 mg vitamin C (or a glass of orange juice) with the iron dose to enhance absorption, especially if iron must be taken with food due to intolerance 2, 4
• Avoid consuming tea, coffee, or calcium-rich foods within 1–2 hours of the iron dose, as these potently inhibit absorption 1, 2, 4
• Discontinue proton-pump inhibitors and H₂-blockers when possible, as they reduce iron absorption 2, 4

Alternative Oral Formulations

• If ferrous sulfate is not tolerated, ferrous fumarate (210–325 mg tablets delivering 69–106 mg elemental iron) or ferrous gluconate (300 mg tablets delivering 37 mg elemental iron) are acceptable alternatives, though evidence does not show improved tolerability 1, 2
• No oral iron formulation has demonstrated superior efficacy or tolerability compared to ferrous sulfate 1, 2

Formulations to Avoid

• Do not prescribe modified-release or enteric-coated iron preparations, as they release iron beyond the duodenum (the primary absorption site) and are classified as "less suitable for prescribing" 1, 2
• Do not rely on multivitamin preparations, which typically contain ≤14 mg elemental iron—insufficient for treating iron deficiency anemia 1, 2

Monitoring Treatment Response

• Check hemoglobin 2 weeks after initiating therapy; an increase of ≥10 g/L predicts treatment success with 90% sensitivity and 79% specificity 1, 2
• Failure to achieve a ≥10 g/L rise at 2 weeks strongly predicts 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 1
• After hemoglobin normalizes, continue oral iron for approximately 3 months to fully replenish bone-marrow iron stores 1, 2

When to Escalate to Intravenous Iron

• Consider IV iron if hemoglobin does not rise after 2–4 weeks of adherent oral therapy; early oral non-responders have only a 21% chance of later response with continued oral iron versus a 65% chance with IV iron 2
• Switch to IV iron when gastrointestinal side effects remain intolerable despite dosing adjustments (alternate-day dosing, taking with food, vitamin C co-administration) 1, 2
• IV iron is indicated in malabsorption syndromes (inflammatory bowel disease, celiac disease, post-bariatric surgery) where oral iron absorption is compromised 1, 2
• Intravenous iron produces a clinically meaningful hemoglobin increase within one week and can replenish total body iron stores in one or two infusions 1, 2

Common Pitfalls to Avoid

• Do not prescribe twice-daily or three-times-daily dosing; this increases gastrointestinal side effects without improving absorption due to hepcidin-mediated blockade 1, 2, 3
• Do not switch between different ferrous salts expecting better tolerability; evidence does not support this practice 1, 2
• Do not discontinue oral iron when hemoglobin normalizes; continue therapy for an additional 3 months to restore iron stores 1, 2

Special Consideration for Chronic Kidney Disease

• If this patient has chronic kidney disease, the dosing recommendation differs: 200 mg elemental iron daily in divided doses (2–3 times per day) is recommended 1
• However, most hemodialysis patients will require intravenous iron on a regular basis to achieve and maintain target hemoglobin levels 1