Oral Iron Dosing in Post-Roux-en-Y Gastric Bypass Patients
Yes—Dosing Must Be Based on Elemental Iron Content
All oral iron prescriptions should specify the dose in milligrams of elemental iron, not the total weight of the iron salt, because different ferrous salts deliver vastly different amounts of absorbable iron per tablet. 1, 2
Why Elemental Iron Matters
- Ferrous sulfate 200 mg provides approximately 65 mg elemental iron per tablet. 1, 2
- Ferrous fumarate delivers 69–106 mg elemental iron per tablet, depending on formulation. 1
- Ferrous gluconate provides only 35–38 mg elemental iron per tablet. 1
- Prescribing by salt weight (e.g., "200 mg ferrous sulfate") without clarifying elemental content can lead to under- or over-dosing if formulations are switched. 1
Recommended Elemental Iron Dose for Post-Bariatric Surgery Patients
Post-Roux-en-Y gastric bypass patients require 45–60 mg elemental iron daily from dedicated iron supplements, not multivitamins alone. 1
- Standard starting regimen: 50–100 mg elemental iron once daily in the morning on an empty stomach. 1, 2
- Bariatric-specific guidance: The duodenal bypass in Roux-en-Y anatomy severely impairs iron absorption, so oral therapy may fail even with optimal dosing. 1
Optimal Dosing Strategy
- Once-daily dosing of 50–100 mg elemental iron is superior to multiple daily doses because doses ≥60 mg trigger hepcidin elevation lasting 24 hours, reducing absorption of subsequent doses by 35–45%. 1, 3
- Alternate-day dosing (100–200 mg elemental iron every other day) markedly increases fractional iron absorption and reduces gastrointestinal side effects while maintaining efficacy. 1, 3
- Morning administration on an empty stomach maximizes absorption. 1, 2, 4
- Co-administer with 100–500 mg vitamin C (or a glass of orange juice) to enhance absorption by forming a soluble iron chelate. 1, 2, 4
Monitoring and When to Escalate to Intravenous Iron
- Check hemoglobin at 2 weeks: An increase of ≥10 g/L predicts treatment success with 90% sensitivity and 79% specificity. 1
- If hemoglobin fails to rise ≥10 g/L by 2 weeks, strongly consider switching to intravenous iron, as this predicts overall oral treatment failure. 1
- Post-bariatric surgery patients are at high risk for oral iron failure due to anatomic disruption of duodenal absorption; intravenous iron should be considered early if oral therapy is ineffective after 4 weeks. 1, 2
Intravenous Iron as First-Line in Bariatric Patients
Intravenous iron is the preferred route when oral iron absorption is anatomically impaired, such as after Roux-en-Y gastric bypass. 1
- Preferred formulations: Ferric carboxymaltose (750–1000 mg per infusion) or ferric derisomaltose (1000 mg single infusion) can replenish total iron deficit in 1–2 visits. 1
- Intravenous iron produces a clinically meaningful hemoglobin rise within one week, far faster than oral therapy. 1
- Safety profile: True anaphylaxis is exceedingly rare (<1%); most adverse reactions are complement-activation-related pseudo-allergic infusion reactions manageable with antihistamines and corticosteroids. 1
Common Pitfalls to Avoid
- Do not prescribe multiple daily doses of oral iron; this increases side effects without improving absorption due to hepcidin blockade. 1, 3
- Do not rely on multivitamins alone for iron repletion; they typically contain only 14–30 mg elemental iron, insufficient for treating deficiency. 1, 2
- Do not continue oral iron indefinitely without monitoring; failure to achieve expected hemoglobin rise by 2 weeks mandates reassessment or escalation to intravenous iron. 1
- Do not use modified-release iron preparations; they release iron beyond the duodenum (the primary absorption site) and are classified as "less suitable for prescribing." 1