Intravenous Monoferric (Ferric Carboxymaltose) – Clinical Use, Dosing, and Monitoring
When to Use IV Ferric Carboxymaltose
Intravenous ferric carboxymaltose (FCM) should replace oral iron when patients cannot tolerate at least two different oral formulations, when ferritin fails to improve after 4 weeks of compliant oral therapy, or when specific malabsorption conditions are present. 1, 2
Absolute Indications for IV Iron Over Oral Therapy
- Active inflammatory bowel disease with hemoglobin <10 g/dL – inflammation-driven hepcidin elevation severely impairs oral iron absorption and oral iron may worsen intestinal inflammation 3, 1, 2
- Post-bariatric surgery patients – duodenal iron absorption is anatomically disrupted 1, 2, 4
- Intolerance to ≥2 different oral iron preparations (e.g., ferrous sulfate and ferrous fumarate or gluconate) 1, 2, 4
- Chronic heart failure with iron deficiency (ferritin <100 ng/mL or ferritin 100–300 ng/mL with transferrin saturation <20%) – IV iron improves exercise capacity, symptoms, and reduces cardiovascular hospitalizations 1, 2
Relative Indications
- Celiac disease with inadequate response to oral iron despite strict gluten-free diet adherence 1, 2
- Chronic kidney disease with functional iron deficiency (ferritin 100–300 ng/mL with transferrin saturation <20%) 1, 2
- Ongoing gastrointestinal blood loss exceeding oral replacement capacity 1, 2
- Severe anemia (hemoglobin <10 g/dL) requiring rapid correction 1, 4
- Cancer-related anemia – inflammation impairs oral absorption 3, 4
Dosing Guidelines for Ferric Carboxymaltose
Standard Dosing Regimen
For patients ≥50 kg: FCM 750 mg IV × 2 doses separated by ≥7 days (total 1,500 mg per course) 5
Alternative single-dose regimen: FCM 15 mg/kg (maximum 1,000 mg) as a single infusion per course in adults 5
For patients <50 kg: FCM 15 mg/kg IV × 2 doses separated by ≥7 days 5
Heart Failure–Specific Dosing
For iron deficiency in heart failure (NYHA class II/III), dosing is weight- and hemoglobin-based 1, 5:
| Weight | Hb <10 g/dL | Hb 10–14 g/dL | Hb >14 to <15 g/dL |
|---|---|---|---|
| <70 kg | Day 1: 1,000 mg Week 6: 500 mg |
Day 1: 1,000 mg Week 6: none |
Day 1: 500 mg Week 6: none |
| ≥70 kg | Day 1: 1,000 mg Week 6: 1,000 mg |
Day 1: 1,000 mg Week 6: 500 mg |
Day 1: 500 mg Week 6: none |
Maintenance dosing: 500 mg at 12,24, and 36 weeks if ferritin <100 ng/mL or ferritin 100–300 ng/mL with transferrin saturation <20% 1, 5
Administration Protocol
- Dilution: FCM must be diluted in 100 mL of normal saline (concentration ≥2 mg iron/mL) 1, 5
- Infusion rate: Administer over 20–30 minutes when diluted 1, 5
- Undiluted push: May give as slow IV push at ~100 mg/min (15 minutes for 1,000 mg dose) 1, 5
- Maximum single dose: 1,000 mg iron per administration 1, 5
- Minimum interval between doses: ≥7 days 1, 5
Monitoring Requirements
Post-Infusion Observation
Observe patients for ≥30 minutes after each infusion for hypersensitivity reactions; this must occur in a setting with resuscitation equipment immediately available 1, 5
Laboratory Monitoring Timeline
- Do NOT recheck iron parameters within 4 weeks of FCM administration – circulating iron interferes with assays, yielding falsely elevated ferritin 1
- Recheck hemoglobin at 2–4 weeks – expect a rise of ~2 g/dL (≥1 g/dL indicates adequate response) 1, 2
- Formal iron reassessment at 3 months – measure ferritin and transferrin saturation to determine need for additional therapy 1
- Long-term surveillance: Recheck iron parameters every 6–12 months in chronic conditions (heart failure, IBD, CKD) 1
Criteria for Additional Iron Therapy
At the 3-month assessment, administer additional FCM if 1:
- Ferritin <100 µg/L, OR
- Ferritin 100–299 µg/L with transferrin saturation <20%
Phosphate Monitoring
Check serum phosphate in patients requiring repeat FCM courses within 3 months – hypophosphatemia occurs in 47–75% of such patients, though most cases are asymptomatic and resolve spontaneously 1, 6
Safety Considerations and Contraindications
Absolute Contraindications
- Hypersensitivity to FCM or any component 1, 5
- Hemoglobin >15 g/dL 1, 5
- Active bacteremia or ongoing infection – discontinue FCM if bacteremia develops 1, 5
Hypersensitivity Reactions
- True anaphylaxis is very rare (0.6–0.7% incidence) 1, 2, 7
- Most reactions are complement-activation pseudo-allergies (infusion reactions) occurring in ~1:200 patients 4, 7
- For mild reactions: stop infusion, wait 15 minutes, restart at slower rate 4
- Resuscitation equipment must be immediately available 1, 5
Hypophosphatemia Risk
- FCM has higher hypophosphatemia rates (58%) compared to iron derisomaltose (4%) or iron sucrose (1%) 1
- Most cases are biochemically moderate (serum phosphate 0.32–0.64 mmol/L) and asymptomatic 1
- Avoid FCM in patients requiring frequent repeat infusions – consider alternative formulations 1
Extravasation Precautions
Avoid extravasation – brown discoloration may be long-lasting; if extravasation occurs, discontinue infusion at that site 5
Critical Clinical Pitfalls to Avoid
- Do not delay IV iron in malabsorption states – patients with active IBD, post-bariatric surgery, or celiac disease will not respond to oral iron 1, 2, 4
- Do not recheck iron parameters <4 weeks post-infusion – falsely elevated ferritin will mask inadequate repletion 1
- Do not confuse infusion reactions with true anaphylaxis – most reactions respond to slowing the infusion rate 4, 7
- Do not administer FCM during active infection – iron may promote bacterial growth 3, 1
- Do not assume a single 1,000 mg infusion achieves complete repletion – clinical trials show most patients require 1,500–2,000 mg total 1
- Do not fail to investigate the underlying cause of iron deficiency while providing IV iron 1, 2
Advantages of FCM Over Other IV Iron Formulations
- High single-dose capacity – can deliver 1,000 mg in 15–30 minutes vs. iron sucrose (maximum 200 mg per dose requiring multiple visits) 1, 8
- Fewer clinic visits – typically 1–2 infusions vs. 4–7 visits for iron sucrose 1
- Lower anaphylaxis risk than iron dextran – no reported cases of true anaphylaxis to date with FCM 1
- First IV iron formulation associated with reduced cardiovascular events and hospitalizations in heart failure patients 1
Timing After Blood Transfusion
FCM can be administered immediately after packed red blood cell transfusion once hemodynamic stability is confirmed and post-transfusion hemoglobin is measured to ensure it remains ≤15 g/dL 1
The iron in transfused red cells (150–280 mg per unit) is not bioavailable for erythropoiesis until the cells are phagocytosed after their 100–110 day lifespan, making post-transfusion IV iron beneficial 2