IV Iron Dosing for a 46.8 kg Female Patient
For a 46.8 kg female patient, administer ferric carboxymaltose 15 mg/kg body weight (approximately 700 mg) as a single intravenous dose, which can be repeated after at least 7 days if needed for a total cumulative dose of 1,500 mg per treatment course. 1
Weight-Based Dosing Algorithm
Since this patient weighs less than 50 kg, the FDA-approved dosing for ferric carboxymaltose is weight-based rather than the standard fixed dose used for heavier patients 1:
- Calculate dose: 15 mg/kg × 46.8 kg = 702 mg per dose
- Administration schedule: Two doses separated by at least 7 days 1
- Total course: Up to 1,500 mg cumulative iron per treatment course 1
Preferred IV Iron Formulation
Ferric carboxymaltose (Injectafer) is the optimal choice for this patient because it allows total dose infusion in 1-2 visits, minimizing healthcare encounters and improving compliance 2. Modern total-dose infusion formulations like ferric carboxymaltose, ferric derisomaltose, or low molecular weight iron dextran are preferred over older formulations (iron sucrose, ferric gluconate) that require 4-7 visits for complete repletion 2.
Alternative Formulations if Ferric Carboxymaltose Unavailable:
- Ferric derisomaltose: 20 mg/kg (up to 936 mg for this patient) as single dose, with lower hypophosphatemia risk 2
- Low molecular weight iron dextran: 1,000 mg in 250 mL normal saline over 1 hour after 25 mg test dose 2
- Iron sucrose: Maximum 200 mg per dose, requiring multiple visits (avoid in outpatient settings due to higher reaction risk at therapeutic doses) 3
Administration Protocol
For Ferric Carboxymaltose (~700 mg dose):
- Dilution: Mix in no more than 250 mL sterile 0.9% sodium chloride (concentration ≥2 mg iron/mL) 1
- Infusion time: Minimum 15 minutes 1
- Alternative: Can give undiluted as slow IV push at ~100 mg per minute 1
- No test dose required 1
Critical Safety Measures:
- Monitor for extravasation - brown discoloration can be long-lasting if extravasation occurs 1
- Resuscitation facilities must be available during administration, though hypersensitivity reactions are rare (<1% with modern formulations) 4
- Avoid in patients with active infection 3
Monitoring and Follow-Up
Laboratory Assessment:
- Timing: Check CBC and iron parameters 4-8 weeks after infusion 2
- Expected response: Hemoglobin should increase 1-2 g/dL within 4-8 weeks 2
- Target ferritin: 50 ng/mL in absence of inflammation 2
- Check serum phosphate if repeat course needed within 3 months, as hypophosphatemia occurs in up to 58% with ferric carboxymaltose (though only 4% with ferric derisomaltose) 2, 1
Long-Term Monitoring:
After normalization, monitor hemoglobin every 3 months for 1 year, then at 2 years 5. Continue monitoring if symptoms recur 5.
Common Pitfalls to Avoid
Never administer iron dextran >1,000 mg or iron gluconate >125 mg as rapid bolus - this dramatically increases reaction risk 2. For patients <50 kg, older guidelines suggesting fixed 500-1,000 mg doses 5 are superseded by FDA weight-based dosing of 15 mg/kg 1.
Do not dilute ferric carboxymaltose to <2 mg iron/mL - this compromises stability 1. The solution is stable for 72 hours at room temperature when properly diluted 1.
Avoid checking ferritin immediately after IV iron - levels are falsely elevated; wait 8-10 weeks to assess true iron repletion 5.
When to Consider Repeat Treatment
Repeat treatment is appropriate if iron deficiency anemia recurs 1. For patients with ongoing losses (menstruation, gastrointestinal bleeding), investigate and address underlying causes while providing iron repletion 5.