What is the appropriate dosing and administration of iron dextran for a patient with iron deficiency anemia, considering potential complicating factors such as impaired renal function or gastrointestinal disorders?

Iron Dextran Dosing for Iron Deficiency Anemia

For iron deficiency anemia, administer low-molecular-weight iron dextran (INFeD) after a mandatory 25 mg test dose, using either repeated weekly dosing of 100 mg IV push over 5 minutes for 10 weeks (total 1000 mg) or total dose infusion of the calculated deficit (up to 1000 mg) diluted in 250 mL normal saline over 1 hour. 1, 2, 3

Test Dose Requirements

All patients must receive a test dose before therapeutic dosing:

• Adults: 25 mg (0.5 mL) slow IV push over 2 minutes 1, 3
• Pediatric patients ≤10 kg: 10 mg test dose 4
• Pediatric patients 10-20 kg: 15 mg test dose 4
• Observe for at least 1 hour after test dose before proceeding with therapeutic dose 3
• Emergency medications (epinephrine, diphenhydramine, corticosteroids) must be immediately available 1, 4
• Critical caveat: Fatal anaphylactic reactions have occurred even after uneventful test doses, so the test dose does not guarantee safety 1, 3

Therapeutic Dosing Regimens

Option 1: Repeated Weekly Dosing (Preferred for Most Patients)

• 100 mg IV push over 5 minutes, once weekly for 10 weeks (total 1000 mg) 1, 2
• This approach minimizes dose-related adverse effects (arthralgias, myalgias) which occur more frequently with larger boluses 1
• Maximum single dose should not exceed 100 mg for standard outpatient administration 1

Option 2: Total Dose Infusion (TDI)

• Calculate total iron deficit using standard formula 3
• Maximum total dose: 1000 mg per infusion 5, 2
• Dilute in 250 mL normal saline and infuse over 1 hour 2, 6
• Can repeat if additional iron needed, but maximum daily dose is 2 mL undiluted (100 mg) 3
• TDI is associated with higher rates of delayed reactions (24-48 hours post-infusion) including arthralgia, backache, fever, and malaise 3

Option 3: Intermediate Dosing for Chronic Kidney Disease

• 500-1000 mg diluted in 250 mL normal saline over 1 hour 2, 7
• This regimen is particularly useful for predialysis CKD patients 7
• More cost-effective than multiple smaller doses while maintaining safety 7

Special Population Dosing

Pediatric Hemodialysis Patients (10-dose course):

• ≤10 kg: 25 mg per dose 1, 2
• 10-20 kg: 50 mg per dose 1, 2
• ≥20 kg: 100 mg per dose 1, 2

Pediatric Predialysis/Peritoneal Dialysis:

• ≤10 kg: 125 mg in 75 mL saline 1, 2
• 10-20 kg: 250 mg in 125 mL saline 1, 2
• ≥20 kg: 500 mg in 250 mL saline 1, 2

Monitoring Parameters

Iron studies timing is critical for accuracy:

• Measure transferrin saturation (TSAT) and ferritin no sooner than 7 days after 100-125 mg doses 1
• Wait 14 days after doses ≥1000 mg before measuring iron parameters 1
• Optimal timing for follow-up: 3-4 weeks after last dose 5, 4
• Target levels: TSAT ≥20% and ferritin ≥100 ng/mL 2, 4
• During maintenance therapy: monitor TSAT and ferritin every 3 months 1, 2

Contraindications and Precautions

Absolute contraindications:

• Active infection (withhold IV iron until resolved) 5, 2
• Acute phase of infectious kidney disease 3

Use with extreme caution in:

• Serious liver impairment 3
• Pre-existing cardiovascular disease (adverse reactions may exacerbate complications) 3
• History of multiple drug allergies (increased anaphylaxis risk) 1, 4
• Patients on ACE inhibitors (may increase reaction risk) 3

Adverse Reactions

Immediate reactions (occur during or within minutes of infusion):

• Anaphylaxis-like reactions: <1% incidence but potentially fatal 1, 4
• Common mild reactions (1-2%): hypotension, hypertension, nausea, vomiting, dyspnea 5, 2

Delayed reactions (24-48 hours post-infusion, more common with TDI):

• Arthralgia, myalgia, backache, fever, headache, malaise 3, 6
• Typically resolve within 3-4 days 3
• Occur in up to 13% of patients receiving larger doses 6

Complicating Factors

Impaired Renal Function:

• Hemodialysis patients: Can use maintenance dosing of 250-1000 mg over 12 weeks, given thrice weekly, twice weekly, weekly, or every other week 1, 2
• Iron dextran is not removed by dialysis (tested across 6 different membrane types) 3
• Predialysis CKD: 500 mg weekly for 2 weeks is safe and cost-effective 7

Gastrointestinal Disorders (IBD, Malabsorption):

• IV iron is first-line therapy for active IBD, hemoglobin <10 g/dL, or oral iron intolerance 1
• Total dose infusion of low-molecular-weight iron dextran is safe and effective in IBD (51% hematopoietic response rate) 8
• Oral iron may exacerbate IBD activity and alter intestinal microbiota 1

Cancer Patients with Ongoing Blood Loss:

• Prefer IV iron over oral when blood loss rate exceeds oral replacement capacity 5
• Do not administer on same day as anthracycline chemotherapy or during neutropenia 5

Product Selection

Low-molecular-weight iron dextran (INFeD) is strongly preferred over high-molecular-weight formulations (Dexferrum) due to lower adverse event rates 5, 2. If contraindications to iron dextran exist, consider alternative IV iron products: ferric gluconate (125 mg weekly × 8 doses) or iron sucrose (200 mg every 2-3 weeks), which have lower anaphylaxis risk but cannot be given as total dose infusions 5, 2.