A 58-year-old man with iron deficiency anemia due to chronic GI blood loss (Hb 7.2 g/dL) develops severe nausea, epigastric pain, and constipation after 2 weeks of ferrous sulfate 325 mg daily. He cannot tolerate further oral iron. What is the drug of choice for iron replacement?

Question

Accepted Answer

A. Ferric carboxymaltose 750 mg IV single dose. ## IV Iron in Oral Intolerance

### Indications for Parenteral Iron

**Key Point:** When oral iron is not tolerated due to GI side effects, IV iron is the next step. Ferric carboxymaltose is preferred among IV agents due to rapid infusion, single-dose repletion potential, and lower anaphylaxis risk.

### Comparison of IV Iron Formulations

| Agent | Dose per infusion | Frequency | Half-life | Anaphylaxis risk | Advantage |
| --- | --- | --- | --- | --- | --- |
| **Ferric carboxymaltose** | 750 mg | 1–2 doses | 7–12 h | Very low (<0.1%) | Rapid infusion, complete repletion in 1–2 doses |
| **Iron sucrose** | 200 mg | 3× weekly | 6 h | Very low | Safe in CKD, preferred in dialysis patients |
| **Iron dextran** | 100–500 mg | Daily/weekly | 3–4 weeks | Moderate (0.6–0.7%) | Longer half-life, but obsolete |
| **Ferumoxytol** | 510 mg | 2 doses | 15 h | Low | Rapid infusion, but less available |

**High-Yield:** Ferric carboxymaltose can replicate total iron stores in 1–2 infusions, whereas iron sucrose requires multiple weekly infusions. For non-dialysis patients with oral intolerance, ferric carboxymaltose is preferred.

### Clinical Pearl

**Clinical Pearl:** Iron sucrose is the agent of choice specifically in **chronic kidney disease patients on hemodialysis** because it has minimal risk of anaphylaxis and is used as maintenance therapy. However, in this non-dialysis patient with acute GI intolerance, ferric carboxymaltose is superior due to rapid repletion.

### Mechanism of GI Side Effects

Oral iron causes:
  - Direct mucosal irritation → nausea, vomiting, abdominal pain
  - Increased intestinal permeability → diarrhea or constipation
  - Reactive oxygen species generation → mucosal inflammation

**Mnemonic:** **SCAB** — Sucrose (dialysis), Carboxymaltose (Acute non-dialysis), Both IV.

Answer

B. Iron dextran 100 mg IM daily

Answer

C. Iron sucrose 200 mg IV thrice weekly

Answer

D. Ferrous gluconate 300 mg twice daily

A 58-year-old man with iron deficiency anemia due to chronic GI blood loss (Hb 7.2 g/dL) develops severe nausea, epigastric pain, and constipation after 2 weeks of ferrous sulfate 325 mg daily. He cannot tolerate further oral iron. What is the drug of choice for iron replacement?

Explanation

IV Iron in Oral Intolerance

Indications for Parenteral Iron

Comparison of IV Iron Formulations

Clinical Pearl

Mechanism of GI Side Effects

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Agent	Dose per infusion	Frequency	Half-life	Anaphylaxis risk	Advantage
Ferric carboxymaltose	750 mg	1–2 doses	7–12 h	Very low (<0.1%)	Rapid infusion, complete repletion in 1–2 doses
Iron sucrose	200 mg	3× weekly	6 h	Very low	Safe in CKD, preferred in dialysis patients
Iron dextran	100–500 mg	Daily/weekly	3–4 weeks	Moderate (0.6–0.7%)	Longer half-life, but obsolete
Ferumoxytol	510 mg	2 doses	15 h	Low	Rapid infusion, but less available