What is the recommended dose of iron for an adult patient with iron deficiency anemia undergoing iron transfusion?

Intravenous Iron Dosing for Iron Deficiency Anemia

For adults with iron deficiency anemia requiring intravenous iron, administer a total cumulative dose of 1000-1500 mg of elemental iron, with the higher dose (1500 mg) being more effective at achieving complete iron repletion and reducing retreatment requirements. 1

Oral Iron Therapy (First-Line)

Start with oral iron at 50-100 mg elemental iron once daily taken on an empty stomach (e.g., one ferrous sulfate 200 mg tablet containing 65 mg elemental iron). 2, 3

• Continue oral iron for 2-3 months after hemoglobin normalization to replenish iron stores 2, 3
• Check hemoglobin at 2 weeks: absence of at least 10 g/L rise predicts treatment failure with 90% sensitivity 2, 3
• Recheck hemoglobin every 4 weeks until normalized 2, 3

When to Switch to Intravenous Iron

Reserve IV iron for patients with:

• Severe intolerance to oral iron (GI disturbance) 2, 3
• Malabsorption (celiac disease, post-bariatric surgery, inflammatory bowel disease) 2, 3
• Ongoing blood loss that exceeds oral replacement capacity 2, 3
• Chronic inflammatory conditions (active IBD, chronic kidney disease) 2, 3
• Failure to respond to oral iron after 2 weeks 2, 3

Intravenous Iron Dosing Regimens

Total Dose Calculation

The average iron deficit in IDA patients is approximately 1400-1500 mg of elemental iron. 1 A cumulative dose of 1500 mg results in significantly lower retreatment rates (5.6%) compared to 1000 mg (11.1%, p<0.001). 1

Formulation-Specific Dosing

High-dose formulations (single or two-dose regimens):

• Ferric carboxymaltose: Maximum 1000 mg per infusion or 20 mg/kg (whichever is lower), infused over 15 minutes 2

  • Give 1000 mg, then repeat 1000 mg one week later if total deficit is ≥1500 mg 2, 1

• Ferric derisomaltose: Maximum 20 mg/kg per infusion, infused over 15-30 minutes 2

  • Can give total dose replacement in 1-2 infusions 2

• Low molecular weight iron dextran: Maximum 20 mg/kg per infusion, infused over 4-6 hours 2

  • Requires test dose of 25 mg IV first 2
  • Can give total dose replacement in single infusion but longer infusion time makes this less practical 2, 4

Low-dose formulations (multiple-dose regimens):

• Iron sucrose: Maximum 200 mg per infusion, infused over 30 minutes 2

  • Requires 5-8 infusions to deliver 1000-1500 mg total 2
  • No test dose required 2

• Ferric gluconate: 125 mg per dialysis session (or 62.5 mg in primary care), infused over 1 hour 5, 6

  • Requires 8-12 infusions to deliver 1000-1500 mg total 5
  • Test dose of 25 mg recommended 2

Practical Dosing Algorithm for Hemodialysis Patients

For chronic kidney disease patients on hemodialysis:

• Give 100-125 mg IV iron at every dialysis session for 8-10 doses (total 800-1250 mg) 2
• Once TSAT ≥20% and ferritin ≥100 ng/mL, maintain with 25-125 mg IV weekly 2
• Monitor TSAT and ferritin every 3 months 2
• Withhold IV iron if TSAT >50% or ferritin >800 ng/mL for up to 3 months 2

Critical Monitoring Parameters

Safety thresholds to prevent iron overload:

• Temporarily withhold IV iron if TSAT >50% or ferritin >800 ng/mL 2
• Resume at reduced dose (one-third to one-half previous dose) when levels normalize 2

Response monitoring:

• IV iron produces clinically meaningful hemoglobin response within 1 week 2, 3
• Check hemoglobin every 4 weeks until normalized 2, 3
• Once normalized, monitor every 3 months for 12 months, then every 6 months for 2-3 years 2

Common Pitfalls to Avoid

Underdosing: The most common error is giving only 1000 mg total when the actual deficit is 1400-1500 mg, leading to incomplete repletion and need for retreatment. 1

Test dose confusion: Only iron dextran formulations require a test dose of 25 mg. 2 Modern formulations (ferric carboxymaltose, ferric derisomaltose, iron sucrose) do not require test doses. 2

Hypophosphatemia risk: Ferric carboxymaltose causes hypophosphatemia in 58% of patients (vs 4% with ferric derisomaltose, 1% with iron sucrose), though most cases are asymptomatic and self-limited. 2

Blood transfusion overuse: Transfusion should be reserved only for severe symptomatic anemia with circulatory compromise, targeting hemoglobin 70-90 g/L (80-100 g/L if unstable coronary disease). 2, 3 Each unit of packed red cells contains only 200 mg elemental iron, insufficient to replenish stores. 2