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

Iron Dextran Dosing for Iron Deficiency Anemia

For adult patients with iron deficiency anemia, low molecular weight iron dextran (INFeD) can be administered as a total dose infusion of 500-1000 mg diluted in 250 mL normal saline over 1 hour after a mandatory 25 mg test dose, making it the most practical option for rapid iron repletion. 1

Dosing Protocols

Total Dose Infusion (Preferred for Rapid Repletion)

• Administer 500-1000 mg as a single infusion diluted in 250 mL of normal saline over 1 hour 1
• This approach is more economical and convenient than multiple smaller doses 1
• Mandatory 25 mg test dose must be given as slow IV push with 1-hour observation before administering the full therapeutic dose 1
• Can be repeated as needed to maintain adequate iron stores 1

Fractionated Dosing (Alternative Approach)

• 100 mg IV over 5 minutes once weekly for 10 doses (total 1000 mg) 1
• This minimizes dose-related arthralgias and myalgias, which occur more frequently with larger boluses 1
• More frequent visits required but lower risk of dose-related adverse effects 1

Critical Safety Considerations

Mandatory Test Dose Protocol

• Always administer 25 mg test dose via slow IV push 1
• Wait 1 hour before proceeding with therapeutic dose 1
• Low molecular weight iron dextran (INFeD) carries a boxed FDA warning for anaphylaxis risk 1

Absolute Contraindications

• Active infection or bacteremia - withhold IV iron therapy 1
• History of anaphylaxis to iron dextran 1

Premedication Strategy

• Consider premedication with diphenhydramine, cimetidine, and dexamethasone to reduce reaction rates, particularly for doses ≥500 mg 2
• Have resuscitation equipment, IV epinephrine, and diphenhydramine immediately available 1

Calculating Total Iron Deficit

The average iron deficit in iron deficiency anemia patients is approximately 1400-1500 mg based on modified Ganzoni formula calculations 3

Modified Ganzoni Formula:

• Dose = 0.0442 × (desired Hgb - observed Hgb) × lean body weight + (0.26 × lean body weight) 1
• If calculated dose exceeds 1000 mg, give remaining dose after 4 weeks if inadequate response 1

Monitoring Parameters

Timing of Laboratory Assessment

• Wait 2 weeks after doses ≥1000 mg before checking iron parameters for accurate assessment 1
• For doses of 100-125 mg weekly, monitoring can occur without interruption 1
• Recheck hemoglobin, ferritin, and transferrin saturation 3-4 weeks after completing therapy 1

Target Parameters

• Transferrin saturation >20% 1
• Serum ferritin >100 ng/mL 1
• Hemoglobin 11-12 g/dL 1

Avoiding Iron Overload

• Withhold iron if transferrin saturation >50% or ferritin >800 ng/mL 1
• Resume at reduced dose (one-third to one-half) once parameters normalize 1

Adverse Effects Management

Common Dose-Related Effects (occur with larger doses)

• Arthralgias and myalgias (most common with doses >100 mg) 1
• Nausea (2.2%), headache, vomiting, chills, backache (1.1% each) 4
• These are not anaphylactic reactions and resolve spontaneously 1

Serious Reactions (Rare)

• Anaphylaxis risk is extremely low with modern low molecular weight preparations 4, 2
• High molecular weight iron dextran (Dexferrum) is off the market due to high adverse event rates 1

Clinical Pitfalls to Avoid

1. Never use high molecular weight iron dextran - only low molecular weight (INFeD) is acceptable 1
2. Do not skip the test dose - this is mandatory despite low anaphylaxis rates 1
3. Avoid checking iron parameters too early after large doses (wait 2 weeks minimum) 1
4. Do not administer during active infection - this is an absolute contraindication 1
5. Inform patients about arthralgias/myalgias with doses >500 mg so they understand this is expected and not an allergic reaction 1

Comparison to Alternative IV Iron Products

While iron dextran allows total dose infusion, newer formulations like iron sucrose (200 mg maximum per dose) and ferric gluconate (125 mg maximum per dose) do not require test doses but necessitate multiple visits to achieve adequate repletion 1. Iron dextran remains the most cost-effective option when total dose infusion is feasible 1.