Dimercaprol

#complete #carded

Related FACEM curriculum (2022) learning objectives:

• ME 3.8.1.6(e) Principles of management of toxicological presentations including: Indications for antidotes
• ME 3.8.2.4 Identify the appropriate antidote or antivenom.

Presentations

• Ampoule: 300 mg dimercaprol, 600 mg benzyl benzoate, 2100 mg peanut oil per 3 mL.

Toxicological Indications

• Arsenic poisoning.
• Inorganic mercury poisoning.
• Gold intoxication.
• Severe lead poisoning or lead encephalopathy (with EDTA).
• Other heavy metal poisoning (e.g., bismuth, antimony, chromium, nickel, tungsten, zinc – limited clinical use).

Contraindications

• Peanut allergy.
• G6PD deficiency.

Pharmacodynamics

• Binds metal ions, forming stable dimercaptides excreted in urine.

Pharmacokinetics

• Not orally absorbed; IM administration only (formulated in peanut oil).
• Peak blood levels: ~30 minutes post-IM injection; rapid distribution.
• Metabolised via glucuronic conjugation; metabolites excreted in urine.
• Dimercaprol–metal conjugates removable by dialysis.

Administration

General

• Administer in intensive care setting.
• Alkalinise urine before treatment to reduce nephrotoxicity (prevents conjugate dissociation).

Dosing

• Severe inorganic arsenic/mercury poisoning:
  • 3 mg/kg IM every 4 hours for 48 hours.
  • Then, 3 mg/kg IM every 12 hours for 7–10 days based on clinical response.
• Lead encephalopathy:
  • Start dimercaprol 4 hours before EDTA.
  • 4 mg/kg IM every 4 hours for 5 days.

Adverse Drug Reactions

• Common (50% incidence):
  • Injection site pain; sterile abscess formation.
  • Fever (especially in children); myalgia.
  • Chest pain; hypertension; tachycardia.
  • Headache, nausea, vomiting.
  • Peripheral paraesthesia; burning lips, mouth, throat, eyes.
  • Lacrimation, rhinorrhoea, excessive salivation.
• Serious:
  • Intravascular haemolysis in G6PD deficiency.
  • Nephrotoxicity (from dissociation of conjugates in acid urine).
  • Hypertensive encephalopathy (supratherapeutic doses).
• Management: Tolerate adverse effects due to severity of poisoning; reduce subsequent doses for life-threatening reactions.

Specific Considerations

• Pregnancy and lactation: Safety unestablished; use if clinically required.
• Paediatric: Same dosing as adults.

Handy Tips

• Never administer intravenously.
• Most effective when given soon after exposure.
• Limit single doses to ≤4 mg/kg due to high adverse effect incidence.
• Use succimer (oral analogue) if the patient is clinically stable.

Pitfall

• Delayed access due to limited availability; only stocked by select hospitals.

Controversy

• Dosing regimens based on historical practices; efficacy poorly defined.