Ferric Carboxymaltose (FCM) for Iron Deficiency Anemia

What is FCM?

Ferric carboxymaltose (brand name: Injectafer) is a third-generation IV iron preparation consisting of a ferric hydroxide core with a carbohydrate shell. It allows high-dose iron repletion in a single rapid infusion — up to 1000 mg in 15 minutes — making it highly convenient compared to older agents.

— Goodman & Gilman's The Pharmacological Basis of Therapeutics

Indications

FCM is FDA-approved for iron deficiency anemia in adults. Key indications include:

Intolerance to oral iron
Malabsorption (sprue, short-bowel syndrome)
Non-adherence to oral therapy
Chronic blood loss (GI, menstrual)
Patients receiving erythropoietin (ESA) therapy
CKD patients (especially on hemodialysis)
Post-bariatric surgery

IV iron can create iron stores in 1–2 sessions, something oral iron would take months to achieve.

— Goodman & Gilman's

Dosing

Patient Weight	Dose	Schedule
≥ 50 kg	750 mg per dose × 2 doses	At least 7 days apart
< 50 kg	15 mg/kg per dose × 2 doses	At least 7 days apart
FDA 2021 update	Single 1000 mg dose	—

Maximum single dose: 750 mg (standard) or 1000 mg (newer FDA approval) Maximum course: 1500 mg per course

— Goodman & Gilman's; National Kidney Foundation Primer on Kidney Diseases 8e

Total Iron Dose Estimation (Ganzoni Formula)

Use this formula to estimate the total iron deficit before therapy:

Total iron dose (mg) = [Actual body weight (kg) × (Target Hb − Actual Hb) × 2.4] + Iron stores (500 mg)

Target Hb is typically 13–15 g/dL for adults
Iron stores replacement = 500 mg (standard)

— Washington Manual of Medical Therapeutics

How to Administer

Route	Details
Intravenous infusion	Dilute in 0.9% NaCl; infuse over ≥ 15 minutes
IV push (undiluted)	Up to 200 mg over at least 10 minutes (for smaller doses)
No test dose required	Unlike iron dextran

Key points:

No premedication required in most patients
Observe patient for at least 30 minutes post-infusion for hypersensitivity reactions
Do not give with active infection/fever (risk of sepsis and adverse reactions)

Pharmacokinetics

Rapidly cleared from circulation after IV administration
~80% distributed to bone marrow, with remainder going to liver and spleen
Leads to transient rise in serum iron, ferritin, and TSAT → followed by correction in Hb levels

Adverse Effects

Common	Serious/Rare
Headache, dizziness	Hypersensitivity / anaphylactoid reaction
Nausea, abdominal pain	Severe hypotension (especially with rapid injection)
Constipation, diarrhea	Hypophosphatemia ⚠️ (a distinctive side effect of FCM)
Rash, injection site reactions	—

The incidence of drug-related adverse events is similar to that of oral ferrous sulfate.

FCM (and ferric derisomaltose) can be associated with significant hypophosphatemia — monitor phosphate levels, especially in patients already at risk.

— Goodman & Gilman's; Washington Manual of Medical Therapeutics

Contraindications & Precautions

Active infection / fever — defer infusion
Iron overload states (hemochromatosis, hemosiderosis)
Withhold if plasma ferritin > 800 μg/L
MRI considerations: Wait at least 1 week after IV iron sucrose/gluconate before MRI; FCM can also transiently alter MRI signal

Comparison with Other IV Iron Agents

Agent	Generation	Max Single Dose	Test Dose?	Notable
Iron dextran	1st	1000 mg	✅ Required	High anaphylaxis risk
Ferric gluconate	2nd	125–250 mg	❌ Not needed	Multiple doses needed
Iron sucrose	2nd	100–300 mg	❌ Not needed	Multiple doses needed
Ferric carboxymaltose	3rd	750–1000 mg	❌ Not needed	Rapid; hypophosphatemia risk
Ferumoxytol	3rd	1020 mg	❌ Not needed	Interferes with MRI
Iron isomaltoside	3rd	1000–1500 mg	❌ Not needed	Single-dose convenience

— Goodman & Gilman's; Washington Manual of Medical Therapeutics

Monitoring After FCM

CBC and reticulocyte count: 2–4 weeks post-infusion
Serum ferritin + TSAT: at 4–8 weeks
Serum phosphate: especially with repeated dosing (FCM-induced hypophosphatemia)
Expect Hb rise within 1–2 weeks; full response in 4–8 weeks

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