What is the recommended dose for iron replacement in a typical adult patient with iron deficiency anemia?

Recommended Dose for Iron Replacement in Adults with Iron Deficiency Anemia

Start with ferrous sulfate 200 mg (65 mg elemental iron) once daily in the morning on an empty stomach, as this is the most cost-effective first-line therapy that optimizes absorption while minimizing side effects. 1, 2

Optimal Oral Iron Dosing Strategy

Standard First-Line Regimen

• Prescribe 50-100 mg of elemental iron once daily rather than multiple daily doses, as this maximizes fractional absorption and reduces gastrointestinal side effects 3, 1, 2
• Ferrous sulfate 200 mg tablets (providing 65 mg elemental iron) remain the gold standard at approximately $1.00 for a 28-day supply 3, 1
• Take iron in the morning on an empty stomach to maximize absorption, though this may increase GI side effects 3, 2

Why Once-Daily Dosing is Superior

• Oral iron doses ≥60 mg stimulate hepcidin elevation that persists for 24-48 hours, blocking subsequent iron absorption by 35-45% 3, 1, 4
• Taking a second dose the same day provides no additional benefit but significantly increases side effects 2, 4
• Multiple daily doses are contraindicated based on current understanding of iron absorption physiology 1, 2

Monitoring Response and Treatment Duration

Expected Timeline

• Hemoglobin should increase by at least 10 g/L (1 g/dL) within 2 weeks of starting therapy—failure to achieve this strongly predicts treatment failure (sensitivity 90.1%, specificity 79.3%) 1, 2, 4
• Monitor hemoglobin within the first 2-4 weeks to confirm adequate response and detect non-responders early 1, 2
• Continue treatment for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of bone marrow iron stores 3, 1, 2

Alternative Strategies for Intolerance

If Standard Dose Not Tolerated

• Switch to alternate-day dosing with 100-200 mg elemental iron rather than changing iron salts, as this significantly increases fractional absorption compared to daily dosing due to hepcidin regulation 3, 2, 4, 5
• Switching between different ferrous salts (ferrous fumarate, ferrous gluconate) is not supported by evidence for improving tolerability 2, 4
• Consider ferric maltol 30 mg twice daily for patients with previous intolerance to traditional iron salts, though it costs $47.60 versus $1.00 for ferrous sulfate per 28 days 2, 4

Strategies to Enhance Absorption

• Take iron with 250-500 mg vitamin C (ascorbic acid) to enhance absorption by forming a chelate with iron 3, 1, 4
• Avoid tea, coffee, or calcium-containing products within 1 hour of iron intake, as these reduce absorption by up to 50% 3, 2, 4
• Do not use H2-blockers or proton pump inhibitors concurrently, as they impair iron absorption 1

When to Escalate to Intravenous Iron

Clear Indications for IV Iron

• Consider IV iron when oral iron is not effective after 2-4 weeks, not absorbed, or not tolerated despite dose modifications 3, 1, 2
• IV iron should be first-line in patients with chronic inflammatory conditions (IBD, CKD, heart failure), continuing blood loss, impaired absorption (post-bariatric surgery, celiac disease), or severe anemia 3, 1, 6
• Parenteral iron produces a clinically meaningful hemoglobin response within one week and can replenish total body iron stores in 1-2 infusions with modern preparations 1, 2

IV Iron Dosing Options

• Ferric carboxymaltose: 750-1000 mg as a single dose or 750 mg twice one week apart 3
• Low-molecular-weight iron dextran: 1000 mg as a single dose 3
• Ferric gluconate: 125 mg per dialysis session (up to 8 doses) for dialysis patients 7

Special Population Considerations

Inflammatory Bowel Disease

• Limit elemental iron to no more than 100 mg daily in patients with IBD and mild anemia 3, 2
• Consider parenteral iron for patients with active IBD, as luminal iron may exacerbate disease activity 3, 2

Chronic Heart Failure

• Screen for iron deficiency (ferritin <100 μg/L and/or transferrin saturation <20%) 3
• Intravenous iron is preferred over oral iron in CHF patients, as oral iron may be poorly absorbed due to gut edema and has not demonstrated prognostic benefit 3

Cancer-Associated Anemia

• Iron replacement may be used to improve hemoglobin response and reduce RBC transfusions for patients receiving erythropoiesis-stimulating agents 3
• Baseline and periodic monitoring of iron parameters is recommended 3

Common Pitfalls to Avoid

• Do not prescribe modified-release iron preparations, as they are less suitable for prescribing and deliver iron beyond the duodenum where absorption is optimal 2, 4
• Do not rely on multivitamin preparations as the sole iron source, as they typically contain insufficient elemental iron (up to 14 mg) for treating iron deficiency anemia 2, 4
• Do not defer iron replacement therapy while awaiting diagnostic investigations unless colonoscopy is imminent 2
• Do not continue oral iron indefinitely without monitoring—failure to respond may indicate non-compliance, malabsorption, continued bleeding, or concurrent vitamin B12/folate deficiency 2, 4