In a patient with hemoglobin 7.1 g/dL, ferritin 19 ng/mL, serum iron 20 µg/dL, and transferrin saturation 5%, what is the appropriate oral elemental iron dose?

Oral Iron Dosing for Severe Iron Deficiency Anemia

Administer 100–200 mg of elemental iron once daily in the morning on an empty stomach, with 500 mg of vitamin C, avoiding food, coffee, and tea for at least 1–2 hours. 1, 2, 3

Recommended Dosing Strategy

Standard Dosing

• Prescribe 100–200 mg elemental iron daily as the target dose for adults with iron deficiency anemia, which represents the evidence-based standard across multiple guidelines. 1, 3, 4
• Start with 100 mg elemental iron once daily (e.g., one 325 mg ferrous sulfate tablet containing 65 mg elemental iron, or one 324 mg ferrous fumarate tablet containing 106 mg elemental iron) and increase to 200 mg daily if needed based on severity. 2, 3, 5
• With a hemoglobin of 7.1 g/dL (severe anemia), ferritin of 19 ng/mL, and transferrin saturation of 5%, this patient has profound absolute iron deficiency requiring the higher end of the dosing range—200 mg elemental iron daily. 1, 4, 6

Optimal Timing and Administration

• Take iron once daily in the morning on an empty stomach (1–2 hours before meals), as morning dosing is superior to afternoon or evening administration due to circadian hepcidin elevation that reduces absorption later in the day. 2, 3, 7
• Co-administer with 500 mg vitamin C (ascorbic acid) to enhance absorption, especially critical in severe deficiency states. 2, 3
• Avoid coffee, tea, and calcium-containing foods for at least 1–2 hours after taking iron, as these substances can reduce absorption by up to 50–54%. 2, 3

Why Not Multiple Daily Doses

• Never prescribe divided doses throughout the day, as oral iron doses ≥60 mg stimulate hepcidin elevation that persists for 24 hours and blocks absorption of subsequent doses by 35–45%. 2, 3, 7
• Once-daily dosing maximizes fractional absorption and minimizes gastrointestinal side effects compared to traditional split-dose regimens. 2, 7

Alternative Dosing if Side Effects Occur

Alternate-Day Dosing

• If gastrointestinal side effects (constipation, bloating, nausea) are intolerable, switch to alternate-day dosing (every other day) with 100–200 mg elemental iron. 2, 3, 5
• Alternate-day dosing significantly increases fractional iron absorption (because hepcidin subsides by 48 hours) while reducing side effects, and maintains therapeutic efficacy. 2, 7
• This strategy is particularly useful for patients who cannot tolerate daily dosing but still need oral therapy. 5, 7

Monitoring Response

Short-Term Assessment

• Check hemoglobin at 4 weeks to assess response; expect a rise of at least 10 g/L (1 g/dL) within 2–4 weeks if oral iron is being absorbed adequately. 2, 3
• Absence of hemoglobin rise after 2 weeks strongly predicts treatment failure and should prompt consideration of switching to intravenous iron. 2, 3

Duration of Therapy

• Continue oral iron for approximately 3 months after hemoglobin normalizes to adequately replenish iron stores, not just correct anemia. 2, 3, 6
• Monitor blood counts every 6 months after completing therapy to detect recurrent iron deficiency. 3

When to Switch to Intravenous Iron

Indications for IV Iron

• Switch to IV iron if hemoglobin fails to rise after 2–4 weeks of adherent oral therapy at appropriate doses. 2, 3
• Consider IV iron if oral iron causes intolerable gastrointestinal symptoms despite dosing adjustments (alternate-day dosing, taking with small amounts of food). 2, 3
• IV iron is preferred first-line in patients with malabsorption conditions (celiac disease, inflammatory bowel disease, prior gastric surgery, chronic kidney disease on dialysis) where oral absorption is significantly impaired. 2, 3
• With a hemoglobin of 7.1 g/dL, if this patient has any underlying condition impairing absorption or requires rapid correction, IV iron should be strongly considered as first-line therapy. 1, 3

Special Considerations for This Patient

Severity Assessment

• Hemoglobin 7.1 g/dL represents severe anemia requiring aggressive iron repletion. 1, 4
• Ferritin 19 ng/mL and transferrin saturation 5% confirm absolute iron deficiency with depleted iron stores. 1
• Serum iron 20 µg/dL is profoundly low, further confirming severe iron-restricted erythropoiesis. 1

Practical Prescription

• Prescribe ferrous sulfate 325 mg (65 mg elemental iron) three tablets once daily in the morning to achieve 195 mg elemental iron, or ferrous fumarate 324 mg (106 mg elemental iron) two tablets once daily to achieve 212 mg elemental iron. 1, 3, 8
• Add vitamin C 500 mg to be taken simultaneously with the iron supplement. 2, 3
• Instruct the patient to take on an empty stomach, wait 1–2 hours before eating, and avoid coffee/tea for at least 1–2 hours. 2, 3

Common Pitfalls to Avoid

• Do not prescribe iron multiple times daily—this increases side effects without improving absorption due to hepcidin elevation. 2, 7
• Do not discontinue therapy when hemoglobin normalizes—continue for 3 months to replenish stores. 2, 3
• Do not assume all patients will tolerate or respond to oral iron—monitor closely and switch to IV iron if no response by 2–4 weeks. 2, 3
• Do not supplement with iron if ferritin levels normalize or become elevated—this is potentially harmful. 3