Treatment of Iron Deficiency Anemia
Start with oral ferrous sulfate 200 mg once daily as first-line therapy for most patients with iron deficiency anemia, but switch to intravenous iron for patients with hemoglobin <10 g/dL, active inflammatory bowel disease, intolerance to oral iron, or malabsorption conditions. 1
Oral Iron Therapy: First-Line for Uncomplicated Cases
Ferrous sulfate 200 mg once daily is the preferred oral formulation due to its effectiveness and low cost. 1 Each 324 mg tablet of ferrous sulfate contains 65 mg of elemental iron. 2
Once-daily dosing is superior to multiple daily doses because it improves tolerability while maintaining equivalent efficacy. 1 Multiple daily doses increase gastrointestinal side effects without improving outcomes. 1
Add vitamin C (ascorbic acid) 500 mg with the iron dose to enhance absorption, particularly when response is suboptimal. 1
Continue oral iron for 3 months after hemoglobin normalizes to fully replenish iron stores. 1
Alternative oral formulations (ferrous gluconate or ferrous fumarate) are equally effective if ferrous sulfate is not tolerated. 1
Expected Response and Monitoring
Hemoglobin should rise by approximately 2 g/dL after 3-4 weeks of treatment. 3, 1 An increase of at least 2 g/dL within 4 weeks is an acceptable speed of response. 3
If no response occurs within 4 weeks, assess for non-adherence, malabsorption, or ongoing blood loss, and consider switching to intravenous iron. 1
Monitor hemoglobin and red cell indices every 3 months for the first year, then again after another year. 1
Intravenous Iron: When to Switch Routes
Intravenous iron should be first-line therapy in specific clinical scenarios where oral iron is ineffective or contraindicated. The most recent AGA guidelines (2024) provide clear indications. 3
Absolute Indications for IV Iron
Hemoglobin <10 g/dL in patients with inflammatory bowel disease with active inflammation. 3 IV iron is more effective and better tolerated than oral iron in IBD, with an odds ratio of 1.57 for achieving a 2 g/dL hemoglobin increase. 3
Intolerance to at least two different oral iron preparations. 1
Post-bariatric surgery patients, particularly after Roux-en-Y gastric bypass, due to disrupted duodenal iron absorption. 3 A single dose of IV iron is more effective and better tolerated than oral ferrous fumarate or gluconate in this population. 3
Celiac disease with inadequate response to oral iron despite adherence to a gluten-free diet. 3
Ongoing gastrointestinal blood loss exceeding oral replacement capacity. 1
IV Iron Formulations
Prefer IV iron formulations that can replace iron deficits with 1-2 infusions. 1 Available options include: 3
Ferric carboxymaltose: 500-1000 mg per dose (up to 20 mg/kg body weight), can be delivered within 15 minutes. 3
Iron sucrose: Maximum 200-300 mg per treatment episode, requires repeated dosing. 3
Iron isomaltoside 1000: Large published trials available in IBD patients. 3
Low molecular weight iron dextran: Can be given as total dose infusion but carries higher risk of anaphylaxis and requires test dose. 3
Ferumoxytol: 510 mg doses, must be given as slow infusion (not rapid) due to postmarketing surveillance documenting reactions with rapid infusion. 3
Dosing Strategy for IV Iron
Use a simplified dosing scheme rather than Ganzoni's formula, which is inconvenient, prone to error, and underestimates iron requirements. 3 The simple scheme for ferric carboxymaltose: 3
| Hemoglobin (g/dL) | Body weight <70 kg | Body weight ≥70 kg |
|---|---|---|
| 10-12 (women) or 10-13 (men) | 1000 mg | 1500 mg |
| 7-10 | 1500 mg | 2000 mg |
Special Clinical Scenarios
Inflammatory Bowel Disease
Treat underlying inflammation first to enhance iron absorption and reduce iron depletion. 3 Optimizing medical management of IBD is essential before or concurrent with iron supplementation. 3
IV iron is first-line for active IBD with Hb <10 g/dL. 3
Oral iron may be appropriate only in carefully selected patients with mild anemia (Hb 11.0-11.9 g/dL in women, 11.0-12.9 g/dL in men), clinically inactive disease, and no prior intolerance to oral iron. 3
Post-Bariatric Surgery
IV iron is preferred due to anatomic considerations affecting duodenal iron absorption. 3
Perform esophagogastroduodenoscopy to exclude anastomotic ulcers causing chronic bleeding. 3
Evaluate other micronutrient deficiencies if iron stores are slow to recover. 3
Celiac Disease
Ensure strict adherence to gluten-free diet to improve iron absorption. 3
- Progress to IV iron if oral supplementation fails despite dietary compliance. 3
Portal Hypertensive Gastropathy
Start with oral iron supplementation initially. 3
Switch to IV iron if ongoing bleeding persists without response to oral therapy. 3
Address underlying cirrhosis and portal hypertension with nonselective beta-blockers to reduce portal pressure. 3
Critical Pitfalls to Avoid
Do not continue oral iron indefinitely without response. Reassess after 4 weeks and switch to IV iron if hemoglobin fails to rise. 1
Do not use multiple daily doses of oral iron. Once-daily or alternate-day dosing is better tolerated with similar efficacy. 1
Do not stop iron therapy when hemoglobin normalizes. Continue for 3 months to replenish stores. 1
Do not overlook vitamin C supplementation when oral iron response is suboptimal. 1
Do not fail to identify and treat the underlying cause of iron deficiency while supplementing. 1
When Treatment Fails
If anemia does not resolve within 6 months despite appropriate iron therapy: 1
- Reassess for ongoing blood loss
- Evaluate for malabsorption syndromes
- Consider further gastrointestinal investigation (upper endoscopy and colonoscopy in men and postmenopausal women)
- Verify patient adherence to therapy
- Consider hematology consultation for complex cases