Intravenous Iron for Iron-Deficiency Anemia
Intravenous iron should be used as first-line therapy when hemoglobin is below 10 g/dL, when oral iron is not tolerated or has failed to raise ferritin levels, in patients with active inflammatory bowel disease, after bariatric surgery, or when rapid correction is needed. 1, 2
Specific Indications for IV Iron
Use IV iron instead of oral iron in these situations:
- Hemoglobin < 10 g/dL – requires more rapid correction than oral iron can provide 1, 2
- Previous intolerance to oral iron – gastrointestinal side effects preventing adherence 1
- Failed oral iron trial – ferritin levels fail to rise after adequate oral supplementation 1, 2
- Clinically active inflammatory bowel disease – oral iron is poorly absorbed and may worsen mucosal inflammation 1
- Post-bariatric surgery – duodenal bypass disrupts iron absorption 1, 2
- Chronic kidney disease (non-dialysis) – functional iron deficiency with inflammation 2, 3
- When erythropoiesis-stimulating agents are needed – IV iron enhances ESA response 1, 2
- Ongoing blood loss exceeding oral absorption capacity – such as gastrointestinal angiodysplasia 4
Preferred IV Iron Formulations and Dosing
Choose formulations that allow complete iron repletion in 1-2 infusions to minimize healthcare visits and improve compliance. 1, 2
Recommended First-Line Agents:
Ferric carboxymaltose (Injectafer/Ferinject):
- 1,000 mg as a single 15-minute infusion for patients ≥50 kg 2, 3
- Alternative: 750 mg × 2 doses separated by ≥7 days (total 1,500 mg) 2, 3
- No test dose required 2, 3
- Risk: hypophosphatemia – monitor phosphate levels, especially with repeat dosing within 3 months 3
Ferric derisomaltose or iron isomaltoside 1000:
- Up to 1,000 mg as a single infusion 2
- No test dose required 2
- Comparable safety profile to ferric carboxymaltose 2
Iron sucrose (Venofer):
- 200 mg per dose over 10 minutes 2
- Requires 5 sessions to deliver 1,000 mg total 2
- Well-established safety but less convenient due to multiple visits 2
Avoid:
Low-molecular-weight iron dextran:
- Requires mandatory test dose due to 0.6-0.7% risk of serious reactions 2
- Historical fatalities make newer agents strongly preferred 2
Intramuscular iron:
Simplified Weight-Based Dosing
Use this practical table instead of the error-prone Ganzoni formula: 1, 2
| Hemoglobin (g/dL) | Body weight <70 kg | Body weight ≥70 kg |
|---|---|---|
| 10-12 (women) or 10-13 (men) | 1,000 mg | 1,500 mg |
| 7-10 | 1,500 mg | 2,000 mg |
For hemoglobin <7 g/dL, add an additional 500 mg to the total dose. 2
Administration Protocol
All IV iron must be given in a setting with immediate resuscitation equipment available. 2
- No test dose required for ferric carboxymaltose, ferric derisomaltose, iron sucrose, or ferumoxytol 2
- Infusion reactions are usually complement-activation-related pseudo-allergy, not true anaphylaxis – these are idiosyncratic and can mimic allergic reactions 1, 2
- For mild reactions: stop infusion, wait 15 minutes, restart at slower rate 1
- Avoid diphenhydramine – side effects can be mistaken for worsening reaction 1
- For severe reactions: corticosteroids may help 1
Monitoring and Expected Response
Expected hemoglobin rise: ≥2 g/dL within 4 weeks of IV iron therapy. 1, 2
Monitoring schedule after successful treatment:
Re-treat with IV iron when: 1
- Serum ferritin drops below 100 μg/L, OR
- Hemoglobin falls below 12 g/dL (women) or 13 g/dL (men)
Safety Thresholds
Stop further IV iron when: 1, 2
- Transferrin saturation exceeds 50%
- Serum ferritin exceeds 800 ng/mL – to avoid iron overload
Target ferritin after treatment: 400 μg/L – this level prevents recurrence of iron deficiency for 1-5 years better than lower levels 1
Critical Pitfall
Rapid recurrence of iron deficiency in asymptomatic patients should raise suspicion for subclinical inflammatory activity – particularly in IBD patients where anemia may be the only sign of active disease even when CRP is normal. 1 Address the underlying disease process, not just the iron deficiency.