Pharmacology · Chelating agents
Dimercaprol !
An intramuscular chelator with two sulfhydryl groups that binds arsenic, mercury and lead. In lead encephalopathy it is given before edetate.
Updated 2026-11-01
Also called: British anti-Lewisite (BAL), 2,3-dimercaptopropanol
Mechanism of action
Arsenic, mercury and lead poison cells by binding the sulfhydryl (-SH) groups of enzymes. Dimercaprol has two -SH groups that bind these metals more strongly, preventing or reversing their binding to enzymes. The dimercaprol–metal complex is excreted in urine; it breaks apart in acidic urine, so urine is kept alkaline to protect the kidney. With iron the complex is more toxic than the metal.
- Metals block the -SH groups of enzymes
- Dimercaprol's two -SH groups grab the metal
- Enzymes are freed
- The complex leaves in alkaline urine
Pharmacokinetics
- Absorption
- Given only by deep intramuscular injection
- Elimination
- As metal complexes in urine
Indications
- Arsenic poisoning Arsenic poisoning →
- Elemental and some inorganic mercury poisoning; not for organic (methyl) mercury Mercury poisoning →
- Severe lead poisoning and lead encephalopathy, together with edetate calcium disodium Lead poisoning →
Adverse effects
Common
- Intense pain at the injection site
- Nausea, vomiting and headache
- Burning of the lips, mouth and throat; salivation and tearing
- Muscle aches and tingling of the limbs
Contraindications
- Peanut allergy
- Liver failure
- Methylmercury (organic mercury) poisoning
- Iron poisoning, and concurrent iron therapy
Key interactions
- Iron supplements
- The dimercaprol–iron complex is toxic and increases the risk of kidney injury; they are not combined
What is monitored
- Urine pH and output
- Kidney and liver function
- Blood or urine metal levels
- Haemoglobin if G6PD deficiency is possible
Administration and safety
- Deep intramuscular injection only; never intravenous
- In lead encephalopathy the first dimercaprol dose comes before edetate is started
Nursing care
- Ask about peanut allergy before the first injection
- Check urine pH and keep the patient well hydrated
- Assess injection sites and pain
- Look for the source of exposure (work, home, traditional remedies)
Pregnancy and breastfeeding
Animal and human data are limited (category C in the Colombian guide); it is used when clearly needed, and breastfeeding is avoided.
Test yourself
Think of the answer, then tap the question to see it.
Why is urine kept alkaline during dimercaprol treatment?
The dimercaprol–metal complex dissociates in acid urine and the freed metal injures the kidney.
Why is dimercaprol not used for iron poisoning?
The dimercaprol–iron complex is more toxic than iron, especially to the kidney.
Which allergy must be asked about before giving dimercaprol?
Peanut allergy.
Related conditions
← Back to the class: Chelating agents
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Guía para el Manejo de Emergencias Toxicológicas (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); eEML - Electronic Essential Medicines List (World Health Organization, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.