What is the recommended protocol for ordering intravenous (IV) iron infusion for a patient with severe iron deficiency, indicated by a low ferritin level?

Ordering IV Iron Infusion for Severe Iron Deficiency (Ferritin 3 ng/mL)

A patient with a ferritin of 3 ng/mL has severe absolute iron deficiency and requires intravenous iron therapy, with a total cumulative dose of 1,500 mg being the most appropriate initial treatment based on calculated iron deficit.

Initial Assessment Required

Before ordering IV iron, you must obtain:

• Complete blood count to determine hemoglobin level, as this directly impacts dosing calculations 1, 2
• Transferrin saturation (TSAT) to confirm absolute iron deficiency (typically <20% with ferritin <100 ng/mL) 1, 3
• Patient weight, as dosing is weight-based for patients <50 kg 2
• Baseline serum phosphate level, as hypophosphatemia occurs in 51-74% of patients receiving ferric carboxymaltose 4, 5

Recommended IV Iron Formulation and Dosing

Ferric carboxymaltose (FCM) is the preferred formulation due to its ability to deliver high doses rapidly with excellent safety profile 2, 6, 4.

For Patients ≥50 kg (Standard Dosing):

• Total cumulative dose: 1,500 mg administered as 750 mg IV on Day 1, followed by 750 mg IV at least 7 days later 2, 7
• Alternative single-dose option: 1,000 mg IV as a one-time dose, though this may be insufficient for complete iron repletion 2, 7

For Patients <50 kg:

• Dose: 15 mg/kg body weight administered in two doses separated by at least 7 days 2

Rationale for 1,500 mg Total Dose:

The average calculated iron deficit in patients with severe iron deficiency anemia is approximately 1,400-1,500 mg 7. Studies demonstrate that 1,000 mg cumulative doses result in significantly higher retreatment rates (11.1%) compared to 1,500 mg doses (5.6%, p<0.001) 7. A 1,500 mg total dose more accurately replaces the actual iron deficit and reduces the need for repeat treatment 7.

Administration Protocol

Preparation:

• Undiluted slow IV push: Administer at 100 mg (2 mL) per minute; for 750 mg dose, this takes approximately 7.5 minutes 2
• IV infusion option: Dilute up to 1,000 mg in no more than 250 mL of 0.9% sodium chloride (minimum concentration 2 mg iron/mL), infuse over at least 15 minutes 2

Safety Monitoring:

• Observe patient for at least 30 minutes post-infusion for hypersensitivity reactions, which occur in <1% of patients 2, 4
• Monitor injection site carefully to avoid extravasation, which causes long-lasting brown skin discoloration 2

Contraindications to Screen For

Do not administer IV iron if patient has:

• Known hypersensitivity to FCM or other parenteral iron products 1, 2
• Active bacteremia or ongoing infection (defer treatment until infection controlled) 1
• Anemia not due to iron deficiency 1, 2
• Evidence of iron overload 1, 2

Post-Treatment Monitoring

At 3 Months:

• Recheck ferritin, hemoglobin, and serum phosphate 1, 2
• Target ferritin level: 100-400 ng/mL for sustained iron stores 1
• Expected hemoglobin increase: median 5.7 g/dL after 1,500 mg iron 8

Ongoing Surveillance:

• Monitor for iron deficiency recurrence every 3 months for the first year, then every 6-12 months 1
• Reinitiate IV iron when ferritin drops below 100 ng/mL or hemoglobin falls below 12 g/dL (women) or 13 g/dL (men) 1

Critical Pitfall: Hypophosphatemia

Ferric carboxymaltose causes hypophosphatemia in 51% of patients, with 13% developing severe hypophosphatemia (<0.32 mmol/L) 5. This complication:

• Correlates with FCM dose (higher with 1,500 mg vs. 1,000 mg) 5
• Can persist for up to 6 months 5
• May cause persistent fatigue despite anemia correction, bone pain, osteomalacia, and fractures 4, 5

Check serum phosphate levels before repeat dosing, especially if repeat treatment occurs within 3 months 2. Treat hypophosphatemia as medically indicated 2.

Why Not Oral Iron?

Oral iron is inappropriate for ferritin of 3 ng/mL because:

• Absorption is severely limited in severe iron deficiency 1
• Requires >6 months to achieve iron repletion 1
• Gastrointestinal side effects occur in up to 60% of patients 1
• IV iron demonstrates superior efficacy for hemoglobin and ferritin improvement compared to oral formulations 1

Sample Order

"Ferric carboxymaltose (Injectafer) 750 mg IV slow push over 7.5 minutes. Repeat dose of 750 mg IV in 7-14 days. Monitor patient for 30 minutes post-infusion. Check CBC, ferritin, TSAT, and serum phosphate at 3 months."