What is the recommended dose of ferrous sulfate (iron supplement) for an adult patient with iron deficiency anemia?

Recommended Dose of Ferrous Sulfate for Iron Deficiency Anemia

The recommended dose is ferrous sulfate 200 mg (containing 65 mg elemental iron) taken once daily in the morning on an empty stomach. 1, 2

Optimal Dosing Strategy

Once-daily dosing is superior to multiple daily doses because oral iron doses ≥60 mg stimulate hepcidin levels that remain elevated for 24-48 hours, blocking subsequent iron absorption by 35-45% and increasing gastrointestinal side effects without improving efficacy. 2, 3 The British Society of Gastroenterology guidelines explicitly state that 50-100 mg of elemental iron once daily (equivalent to one ferrous sulfate 200 mg tablet) taken in the fasting state represents the best compromise for initial treatment. 1

Timing and Administration

• Take iron in the morning on an empty stomach to maximize absorption, though this may increase gastrointestinal side effects. 2
• Avoid taking iron with food, tea, coffee, or calcium-containing products, as these reduce iron absorption by up to 50%. 2
• Do not give afternoon or evening doses after a morning dose, as the circadian increase in plasma hepcidin is augmented by morning iron, reducing absorption of subsequent doses. 3

Alternative Dosing for Intolerance

If the standard daily dose is not tolerated, reduce to one tablet every other day rather than switching to a different iron salt. 2 Alternate-day dosing with 100-200 mg elemental iron significantly increases fractional iron absorption compared to daily dosing due to hepcidin regulation. 2, 3 Research demonstrates that oral iron doses ≥60 mg stimulate an acute increase in hepcidin that persists 24 hours but subsides by 48 hours, making alternate-day dosing physiologically rational. 3

Alternative options for persistent intolerance include:

• Ferric maltol 30 mg twice daily 2
• Parenteral iron for patients with contraindications, ineffectiveness after adequate trial, or intolerance despite dose modifications 2

What NOT to Do

• Do not prescribe multiple daily doses of iron, as this increases side effects without improving absorption due to hepcidin-mediated blockade. 2
• Do not use modified-release iron preparations as the sole iron source, as these are considered less suitable for prescribing. 1, 2
• Do not assume that switching between different ferrous salts will improve tolerability—this practice is not supported by evidence. 1, 2

Monitoring and Treatment Duration

Monitor hemoglobin response within the first 2-4 weeks of starting treatment—an increase of at least 10 g/L after 2 weeks is expected in responding patients (sensitivity 90.1%, specificity 79.3% for adequate subsequent response). 1, 2 The absence of this response is strongly predictive of subsequent treatment failure. 1

Continue oral iron for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of bone marrow iron stores. 1, 2 After iron repletion, monitor blood counts every 3 months for 12 months, then every 6 months for 2-3 years to detect recurrent iron deficiency anemia. 1, 2

Special Considerations

Inflammatory Bowel Disease

For patients with inflammatory bowel disease and mild anemia, limit elemental iron to no more than 100 mg daily, and consider parenteral iron for patients with active inflammatory bowel disease, as luminal iron may exacerbate disease activity and alter intestinal microbiota. 2

When to Consider Parenteral Iron

Parenteral iron should be considered when oral iron is contraindicated, ineffective after an adequate trial, or not tolerated despite dose modifications. 2 Modern formulations can deliver 500-1000 mg in a single 15-30 minute infusion without requiring a test dose. 2 In patients with chronic disease, continuing blood loss, impaired absorption, or gastrointestinal inflammatory pathology, parenteral iron is more effective than continuing traditional oral therapy. 1

Common Pitfalls

• Do not defer iron replacement therapy while awaiting diagnostic investigations unless colonoscopy is imminent. 2
• Do not overlook the need for continued monitoring after hemoglobin normalization, as recurrent anemia may indicate persistent disease activity. 2
• Remember that packed red cell transfusion should be reserved for severe symptomatic anemia or hemodynamic instability, not routine iron deficiency anemia treatment. 1, 2