How to administer iron in ida
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Here is a complete guide on iron administration in IDA, drawn from Goodman & Gilman's Pharmacological Basis of Therapeutics, Katzung's Basic and Clinical Pharmacology, and Goldman-Cecil Medicine.
Iron Administration in Iron Deficiency Anemia (IDA)
1. Oral Iron (First-line)
Preferred salts - ferrous (Fe²+) salts, as ferrous iron is absorbed ~3x better than ferric salts:
| Preparation | Tablet Size | Elemental Iron | Usual Adult Dose |
|---|---|---|---|
| Ferrous sulfate (hydrated) | 325 mg | 65 mg | 2-4 tablets/day |
| Ferrous sulfate (desiccated) | 200 mg | 65 mg | 2-4 tablets/day |
| Ferrous gluconate | 325 mg | 36 mg | 3-4 tablets/day |
| Ferrous fumarate | 325 mg | 106 mg | 2-3 tablets/day |
Dosing goal: 200-400 mg of elemental iron per day delivers the maximum tolerable amount. About 25% of oral ferrous iron is absorbed, translating to 40-60 mg of usable iron per day - enough for 2-3x normal red cell production.
How to take:
- Best absorbed on an empty stomach
- Taking with meat protein or vitamin C increases absorption
- Avoid concurrent calcium, fiber, tea (reduces absorption by up to 90%), and coffee (reduces absorption ~60%)
- Avoid dairy with tablets
Monitoring response:
- Reticulocyte count rises within 1 week
- Hemoglobin begins rising by week 2
- Assess effectiveness at 4 weeks - a rise of ≥2 g/dL confirms response
- Continue iron until ferritin reaches 50-100 ng/mL (stores fully replete)
Side effects: Nausea, epigastric discomfort, abdominal cramps, constipation, diarrhea (all dose-related). Black stools are common and clinically insignificant. To manage: lower the dose, take with food, or switch to a different ferrous salt.
Lower doses work too: As little as 15-20 mg elemental iron daily can be effective with fewer GI side effects (Goldman-Cecil).
2. Parenteral Iron (IV or IM)
Indications - use when:
- Cannot tolerate or absorb oral iron
- Ongoing bleeding exceeds oral replacement capacity
- Malabsorption (celiac disease, post-gastrectomy, bariatric surgery, bowel resection, IBD)
- H. pylori infection or autoimmune gastritis impairing absorption
- Advanced CKD on hemodialysis + erythropoietin therapy
- Pregnancy (IV iron is superior to oral)
- No response to oral iron within 2 weeks
Available IV formulations:
| Agent | Dose | Administration |
|---|---|---|
| Low-molecular-weight iron dextran | 1000 mg | Over 1 hour (single replacement dose) |
| Ferumoxytol | 510 mg | Over 15 min, repeated once in 3-8 days |
| Ferric carboxymaltose | 750-1000 mg | Two 750 mg doses 1 week apart |
| Ferric derisomaltose | Up to 1000 mg | Over 20 minutes |
| Sodium ferric gluconate complex | Lower doses | Slower infusion (older agent) |
| Iron sucrose | Lower doses | Infusion (older agent) |
IM route (iron dextran only): Deep IM injection is an option but causes local pain and tissue staining; the IV route is strongly preferred.
Iron dextran - special precaution: Always give a test dose first (risk of hypersensitivity/anaphylaxis). High-molecular-weight formulations carry a higher anaphylaxis risk than low-molecular-weight forms.
Infusion reactions: Not true allergy - caused by complement activation by labile free iron ("complement activation-related pseudoallergy"). Rate of mild reactions: ~1 in 200; major reactions: ~1 in 200,000. Diphenhydramine premedication should be avoided as it can worsen symptoms.
Post-infusion management:
- Observe all patients for 30 minutes after infusion
- Mild reaction: stop infusion, resume at slower rate
- Severe reaction / anaphylaxis: IV fluids (500 mL normal saline), hydrocortisone 150-500 mg IV, and epinephrine (IV 1 mL of 1:10,000 or IM 0.3-0.5 mL of 1:1000)
Special notes:
- Ferumoxytol interferes with MRI (functions as contrast agent) - do MRI before or after dosing window
- Ferric carboxymaltose causes hypophosphatemia in ~75% of patients (symptomatic in some)
- Parenteral iron bypasses intestinal regulatory mechanisms, so monitor ferritin and transferrin saturation to avoid iron overload
3. When to Reassess
- If no response to oral iron by 3-4 weeks, do not simply continue - re-evaluate the diagnosis
- Check compliance, GI absorption, ongoing blood loss, or underlying inflammatory disease
- If ferritin falls below 50 ng/dL after an IV infusion course, repeat the infusion
4. Total Iron Dose Calculation
The total iron deficit can be calculated to guide IV replacement dosing (Ganzoni formula):
Total iron deficit (mg) = body weight (kg) × (target Hb - actual Hb) (g/dL) × 2.4 + iron stores (500 mg)
Sources: - Goodman & Gilman's Pharmacological Basis of Therapeutics, pp. 930-933 | - Katzung's Basic and Clinical Pharmacology 16e, pp. 931-933 | - Goldman-Cecil Medicine, pp. 1681-1682
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