Dimercaprol (BAL - British Anti-Lewisite)

Mechanism

Pharmacological Group and Molecular Target

Lipid-soluble bidentate chelating dithiol.

Detailed Mechanism of Action

Heavy metals (such as arsenic, mercury, gold, or lead) exert their cellular toxicity by covalently binding to the sulfhydryl (-SH) groups of essential cellular mitochondrial metabolic enzymes (e.g., pyruvate dehydrogenase), blocking cellular respiration and ATP production. Dimercaprol possesses two reactive sulfhydryl groups on its linear dithiol molecule. These groups compete favorably for the heavy metal, displacing it from cellular tissues and forming a stable non-toxic 5-membered heterocyclic ring that contains the chelated metal, facilitating its passive biliary and renal excretion.

Pharmacokinetics

Pharmacokinetic and Toxicokinetic Profile

• Administration: Only by deep intramuscular (IM) route; formulated exclusively in a 10% oil solution in peanut oil due to its total insolubility in water. Never administer intravenously.
• Distribution: High lipid solubility; It effectively penetrates the intracellular space and crosses the blood-brain barrier.
• Excretion: Biliary (fecal) and urinary in similar proportions.
• Elimination half-life: Very short, less than 2 hours.

Indicators and dose

Specific Clinical Indications

• Severe acute poisoning by symptomatic arsenic or inorganic mercury.
• Treatment of severe acute lead encephalopathy in mandatory combination with Edetate Calcium Disodium to prevent redistribution of lead to brain tissue.

Dosage Scheme and Infusion Protocols

• Arsenic or Mercury Poisoning (Moderate): 2.5 mg/kg by deep IM route every 4 hours for the first two days, subsequently reducing to every 12 hours until completing 10 days of treatment.
• Severe Intoxication with Encephalopathy (Lead): 4 mg/kg by deep IM route every 4 hours associated with Edetate Calcium Disodium administered in a different anatomical site.

Security

Critical Precautions and Contraindications

• Contraindicated in Iron, Cadmium or Selenium Poisoning: The chelates formed by dimercaprol with these metals are highly nephrotoxic and increase their systemic toxicity.
• Food Allergies: Absolutely contraindicated in patients with proven allergy to peanuts due to the vehicle in the formulation.
• Urinary Acidification: Urine must be kept alkaline during chelate excretion, given that the dimercaprol-metal complex tends to dissociate in acidic urinary environments, releasing the free heavy metal and causing acute renal tubular necrosis.