What are the recommended intravenous iron dosing regimens for an adult with iron‑deficiency anemia after bariatric surgery who cannot absorb oral iron?

Intravenous Iron Dosing for Post-Bariatric Surgery Patients

For adults after bariatric surgery who cannot absorb oral iron, intravenous iron is the preferred first-line therapy, with ferric carboxymaltose 750–1000 mg per infusion (two doses ≥7 days apart for a total of 1500 mg) or ferric derisomaltose 1000 mg as a single infusion being the optimal regimens. 1

Why IV Iron is Mandatory After Bariatric Surgery

Post-bariatric surgery patients have profoundly impaired oral iron absorption because:

• Iron is absorbed most efficiently in the duodenum and proximal jejunum, which is bypassed after Roux-en-Y gastric bypass and disrupted after sleeve gastrectomy. 1
• Gastric acid secretion is reduced, impairing the conversion of dietary iron to absorbable ferrous iron. 1, 2
• Chronic inflammation from surgery itself creates a persistent hepcidin elevation that blocks intestinal iron absorption. 2
• Anastomotic ulcers are common and cause chronic occult bleeding, further depleting iron stores. 1

A single dose of IV iron is more effective and better tolerated than oral ferrous fumarate or ferrous gluconate in post-bariatric surgery patients. 1

Recommended IV Iron Formulations and Dosing

First-Line Options (High-Dose, 1–2 Infusion Regimens)

Ferric carboxymaltose (Injectafer):

• 750–1000 mg per 15-minute infusion 1, 3
• Two doses given ≥7 days apart for a total of 1500 mg per course 1, 3
• Alternative single-dose regimen: 15 mg/kg up to 1000 mg as a single infusion 3
• Cost: $3,470 per course 1
• Special caution: Risk of hypophosphatemia, especially with repeated dosing; avoid in patients with poor nutrition or malabsorption 1, 4

Ferric derisomaltose:

• 1000 mg as a single infusion 1
• Cost: $3,896 per course 1
• No hypophosphatemia risk 1

Low-molecular-weight iron dextran:

• 1000 mg as a single infusion 1
• Cost: $405 per course (most cost-effective) 1
• Requires test dose due to higher anaphylaxis risk (0.6–0.7%) 1

Alternative Options (Multiple Infusions Required)

Iron sucrose:

• 200 mg per infusion, 5 doses or 300 mg per infusion, 3 doses weekly 1
• Cost: $441.50 per course 1
• Requires multiple clinic visits 1

Ferumoxytol:

• 510 mg per infusion, 2 doses or 1020 mg as a single dose 1
• Cost: $1,963 per course 1
• Important: Notify radiology if MRI is needed within 3 months, as it acts as an MRI contrast agent 1

Ferric gluconate:

• 125 mg per infusion, 8 doses given no closer than every other day 1
• Cost: $610 per course 1
• Least convenient due to frequent visits 1

Clinical Algorithm for Post-Bariatric Surgery Patients

Step 1: Confirm Iron Deficiency

• Ferritin < 30 ng/mL (or < 100 ng/mL if inflammation present) 1
• Transferrin saturation < 20% 1
• Hemoglobin < 12 g/dL (women) or < 13 g/dL (men) 1

Step 2: Rule Out Ongoing Blood Loss

• Perform esophagogastroduodenoscopy to exclude anastomotic ulcers, which are common after bariatric surgery 1
• Check for other micronutrient deficiencies (vitamin B12, folate) that may blunt response 1

Step 3: Choose IV Iron Formulation

• Prefer 1–2 infusion regimens (ferric carboxymaltose, ferric derisomaltose, or low-molecular-weight iron dextran) to minimize clinic visits and infusion-related risk 1
• Avoid ferric carboxymaltose in patients with poor nutrition or repeated dosing needs due to hypophosphatemia risk 1
• Avoid iron dextran as first-line unless cost is prohibitive, due to higher anaphylaxis risk requiring test dose 1

Step 4: Administer IV Iron Safely

• All IV iron must be given in a facility equipped with resuscitation equipment 1
• Most reactions are complement-activation pseudo-allergies (not true anaphylaxis); manage by stopping infusion, waiting 15 minutes, then restarting at slower rate 1
• Diphenhydramine should be avoided because its side effects can mimic worsening reactions 1
• For severe reactions, corticosteroids may be beneficial 1

Step 5: Monitor Response

• Check hemoglobin at 2–4 weeks; expect a rise of ≈2 g/dL 1
• If iron stores are slow to recover, evaluate for other micronutrient deficiencies or ongoing blood loss 1
• Monitor hemoglobin and ferritin every 3 months for the first year, then annually 1

Step 6: Repeat Treatment as Needed

• IV iron may be repeated if iron deficiency recurs 3
• Post-bariatric patients often require maintenance IV iron indefinitely due to persistent malabsorption 2

Special Considerations for Women of Childbearing Age

• Women after gastric bypass are at highest risk for refractory anemia requiring IV iron 5
• 89.2% of women requiring iron infusions had preoperative anemia 5
• Women with abnormal uterine bleeding require more frequent iron infusions and have persistently lower hemoglobin despite treatment 5
• Consider gynecology consultation for women with menorrhagia to address underlying bleeding source 5

Critical Pitfalls to Avoid

• Do not persist with oral iron in post-bariatric surgery patients; it is ineffective due to anatomic disruption of duodenal absorption 1
• Do not use ferric carboxymaltose repeatedly without monitoring phosphate levels; prolonged hypophosphatemia can cause fatigue and osteomalacia 1
• Do not assume a single IV iron course is sufficient; post-bariatric patients often require indefinite maintenance therapy 2
• Do not overlook anastomotic ulcers as a source of ongoing blood loss; perform endoscopy if anemia persists 1
• Do not forget to screen for vitamin B12 and folate deficiency, which commonly coexist and blunt hematologic response 1

Alternative: Oral Sucrosomial Iron (If IV Access is Problematic)

• Oral sucrosomial iron has a unique absorption mechanism that may bypass duodenal malabsorption 6
• In a small study, switching from IV iron to oral sucrosomial iron maintained stable hemoglobin and ferritin levels over 3 months 6
• This may be considered as an alternative in patients who cannot access IV therapy, though evidence is limited 6