What is the recommended dosage and treatment duration for iron deficiency anemia using oral iron supplements like ferrous sulfate?

Oral Iron Supplementation for Iron Deficiency Anemia

First-Line Treatment Recommendation

For iron deficiency anemia, start with ferrous sulfate 200 mg once daily (containing approximately 65 mg elemental iron), which is as effective as higher divided doses but with significantly fewer gastrointestinal side effects. 1, 2

Optimal Dosing Strategy

Standard Dosing

• Ferrous sulfate 200 mg once daily is the gold standard due to proven efficacy, low cost, and equivalent effectiveness to more expensive formulations 2
• The dose provides 50-100 mg elemental iron, which is sufficient for most patients 2, 3
• Take on an empty stomach in the morning for maximum absorption, as food reduces absorption by up to 50% 2
• Multiple daily doses increase side effects without improving absorption 1, 2

Alternative Dosing for Intolerance

• If gastrointestinal side effects occur, switch to alternate-day dosing (200 mg every other day), which produces similar hemoglobin responses with significantly lower nausea rates 1, 2, 4
• Lower doses (100 mg ferrous sulfate once daily) may be equally effective and better tolerated 1, 5
• Other ferrous salts (ferrous fumarate, ferrous gluconate) are equally effective alternatives 1

Enhancement of Absorption

• Consider adding ascorbic acid 250-500 mg twice daily with iron to enhance absorption, though data on clinical effectiveness are limited 1, 2

Treatment Duration

Continue oral iron for 3 months after hemoglobin normalization to replenish iron stores. 1, 2

• Hemoglobin should increase by at least 1-2 g/dL after 3-4 weeks of treatment 1, 2
• Expected rise is approximately 2 g/dL within the first month 2
• If hemoglobin increases by at least 10 g/L after 2 weeks, this predicts adequate response with 90% sensitivity 2

Monitoring Parameters

Initial Response Assessment

• Check hemoglobin at 2 weeks to assess initial response 1, 2
• Recheck at 4 weeks to confirm adequate response 1
• Failure to respond is usually due to poor compliance, misdiagnosis, continued blood loss, or malabsorption 1

Long-Term Monitoring

• After normalization, monitor hemoglobin and red cell indices every 3 months for 1 year 1, 2
• Then recheck after another year 1
• Subsequently monitor if symptoms of anemia develop 1
• Recurrence occurs in over 50% of patients after 1 year, often indicating ongoing intestinal inflammation 1

When to Use Intravenous Iron

Switch to intravenous iron in the following situations: 1, 2

• Intolerance to at least two oral iron preparations 1
• Non-response to oral iron (inadequate hemoglobin rise after 2 weeks) 1, 2
• Severe anemia (hemoglobin <10 g/dL) 1
• Active inflammatory bowel disease 1, 2, 3
• Malabsorption conditions (celiac disease, post-bariatric surgery) 3
• Ongoing blood loss 1, 2
• Need for rapid correction prior to surgery 6

Intravenous Options

• Ferric carboxymaltose: 1000 mg maximum single dose over 15 minutes 1, 6
• Iron sucrose: 200 mg over 10 minutes 1
• Iron dextran: 20 mg/kg over 6 hours (higher risk of anaphylaxis at 0.6-0.7%) 1
• Intravenous iron produces faster initial hemoglobin rise, but at 12 weeks the rise is similar to oral therapy 1

Common Pitfalls to Avoid

• Do not prescribe three-times-daily dosing – this outdated regimen increases side effects without improving absorption 1, 2
• Do not defer iron replacement while awaiting investigations unless colonoscopy is imminent 1
• Do not use intramuscular iron – it is painful, requires multiple injections, and has no clear advantage over oral or intravenous routes 1
• Do not rely on faecal occult blood testing – it is insensitive and non-specific for diagnosing iron deficiency anemia 1
• Avoid afternoon or evening dosing after a morning dose, as circadian hepcidin increases reduce absorption 4

Special Considerations

Inflammatory Bowel Disease

• Intravenous iron is preferred for active disease due to concerns that oral iron may exacerbate inflammation through reactive oxygen species generation 1, 2
• Oral iron (100 mg/day maximum) may be used only in mild anemia with clinically inactive disease 1, 2

Pregnancy

• Intravenous iron is indicated during second and third trimesters when oral iron is not tolerated or ineffective 3

Chronic Kidney Disease and Heart Failure

• These conditions often involve functional iron deficiency requiring parenteral therapy 1, 3
• Refer to specialist guidelines for management 1