Recommended Iron Supplementation Dose for Iron Deficiency Anemia
For adults with iron deficiency anemia, start with 50-100 mg of elemental iron once daily (e.g., one ferrous sulfate 200 mg tablet containing 65 mg elemental iron), taken in the morning on an empty stomach. 1, 2
Initial Dosing Strategy
Once-daily dosing is superior to multiple daily doses because oral iron doses ≥60 mg stimulate hepcidin elevation that persists for 24-48 hours, blocking subsequent iron absorption by 35-45% and increasing gastrointestinal side effects without improving efficacy. 2, 3
Ferrous sulfate 200 mg tablets (providing 65 mg elemental iron) are the most practical and cost-effective first-line option, taken as one tablet daily in the fasting state. 1, 2, 4
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
Alternative Dosing for Intolerance
If standard daily dosing is not tolerated, switch to alternate-day dosing (one tablet every other day) rather than changing to a different iron salt, as alternate-day dosing with 100-200 mg elemental iron significantly increases fractional iron absorption compared to daily dosing due to hepcidin regulation. 1, 2, 3
Do not switch between different ferrous salts (sulfate, fumarate, gluconate) for intolerance, as this practice is not supported by evidence. 1, 2
Alternative options for persistent intolerance include ferric maltol (30 mg twice daily) or parenteral iron. 1, 2
Monitoring Response
Check hemoglobin after 2 weeks of treatment—an increase of at least 10 g/L is strongly predictive of adequate response (sensitivity 90.1%, specificity 79.3%). 1, 2
Monitor hemoglobin every 4 weeks until normalized, then continue oral iron for 2-3 months after hemoglobin normalization to replenish iron stores. 1, 2
After iron repletion, monitor blood counts every 3 months for the first year, then every 6 months for 2-3 years to detect recurrent iron deficiency anemia. 1, 2
Special Populations
Inflammatory Bowel Disease
For patients with inflammatory bowel disease and inactive disease, limit elemental iron to no more than 100 mg daily. 1, 2
For patients with active inflammatory bowel disease, avoid oral iron and use parenteral iron instead, as luminal iron may exacerbate disease activity and alter intestinal microbiota. 1, 2
Chronic Kidney Disease
- For non-dialysis chronic kidney disease patients, oral iron should be administered at a daily dose of at least 200 mg of elemental iron for adults, though these patients may not maintain adequate iron status with oral iron alone. 1
When to Use Parenteral Iron
Consider parenteral iron when oral iron is contraindicated, ineffective after an adequate trial (no hemoglobin rise ≥10 g/L after 2 weeks), or not tolerated despite dose modifications. 1, 2
Parenteral iron is more effective than oral iron in patients with chronic disease, continuing blood loss, impaired absorption, or gastrointestinal inflammatory pathology. 1
Modern parenteral iron formulations (ferric carboxymaltose, ferric derisomaltose) can deliver 500-1000 mg in a single 15-30 minute infusion without requiring a test dose. 1, 2
Critical Pitfalls to Avoid
Do not prescribe multiple daily doses (e.g., twice or three times daily dosing per FDA labeling 4), as this increases side effects without improving absorption due to hepcidin-mediated blockade. 2, 3
Do not use modified-release iron preparations, as they are less suitable for prescribing and deliver iron beyond the duodenum where absorption is optimal. 1, 2
Do not defer iron replacement while awaiting diagnostic investigations unless colonoscopy is imminent. 2
Blood transfusion should be reserved for severe symptomatic anemia or hemodynamic instability, as parenteral iron reliably produces a clinically meaningful hemoglobin response within one week. 1, 2