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Answer to E part
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I now have all the information needed for a complete answer to Part (e).
Answer to Part (e): Iron Poisoning - Antidote, Route of Administration, and Contraindicated Chelating Agent
Antidote for Iron Poisoning
Desferrioxamine (Deferoxamine) is the antidote of choice for iron poisoning.
- It is isolated from Streptomyces pilosus
- It binds iron avidly by forming a stable chelate complex called ferrioxamine
- 1 g of desferrioxamine chelates approximately 85 mg of iron
- The iron-chelator complex is excreted in the urine, often turning it an orange-red (vin rose) color - this is used as a positive test for significant iron absorption
Routes of Administration and Doses
| Route | Dose | Purpose |
|---|---|---|
| Intragastric (via stomach tube) | 5-10 g dissolved in 100 mL distilled water, instilled at end of lavage | Binds unabsorbed iron in the stomach |
| Intramuscular (IM) | 1 g initially, then 500 mg every 4-12 hours (max 6 g/24 hr) | For moderate poisoning |
| Intravenous (IV) | 15 mg/kg/hour by infusion (max 60-80 mg/kg/24 hr) | For severe poisoning with systemic toxicity |
Preferred route: IV infusion in severe cases, as oral absorption of deferoxamine is poor and may paradoxically increase iron absorption when given orally. Therefore, the parenteral route is the route of choice for systemic iron toxicity.
- Katzung's Basic and Clinical Pharmacology, 16th Ed., p. 2818
- P C Dikshit Textbook of Forensic Medicine and Toxicology, p. 479
Rationale for Deferoxamine
- It chelates free ferric iron (Fe³+) in plasma and tissues, converting it to the non-toxic, water-soluble ferrioxamine complex
- It does NOT compete for biologically chelated iron in hemoglobin, cytochromes, or hemoproteins - so it does not disrupt essential iron-dependent enzymes
- The ferrioxamine complex is renally excreted, effectively eliminating iron from the body
Chelating Agent Contraindicated in Iron Poisoning
BAL (British Anti-Lewisite / Dimercaprol) is contraindicated in iron poisoning.
Why?
- BAL (dimercaprol) forms a toxic iron-BAL complex that is nephrotoxic and can cause redistribution of iron to the brain, worsening toxicity rather than reducing it
- The BAL-iron chelate is unstable at acidic urine pH and may dissociate, releasing free iron again in the kidneys
- This makes BAL potentially dangerous - it redistributes iron to sensitive tissues rather than safely eliminating it
CaNa2-EDTA is also considered contraindicated or unhelpful in iron poisoning because:
- It can mobilize iron along with other endogenous metals (zinc, manganese) and the iron-EDTA complex may actually increase systemic iron distribution rather than aiding its elimination
- Goodman & Gilman's Pharmacological Basis of Therapeutics notes that CaNa2EDTA mobilizes iron among several endogenous metallic cations, making it unsuitable as an antidote
Summary Table
| Feature | Details |
|---|---|
| Antidote of choice | Desferrioxamine (Deferoxamine) |
| Route (severe cases) | IV infusion - 15 mg/kg/hr |
| Route (moderate) | IM - 1 g initially, then 500 mg 4-12 hourly |
| Route (gut decontamination) | Intragastric via stomach tube - 5-10 g |
| Urine color on treatment | Orange-red (vin rose) - confirms significant iron absorption |
| Contraindicated chelator | BAL (Dimercaprol) |
| Reason for contraindication | Forms toxic iron-BAL complex; redistributes iron to brain and kidneys; nephrotoxic |
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