Sodium calcium edetate

#completed #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.

Presentation

• Sodium calcium edetate 1 g/5 mL ampoules.

Toxicological Indications

• Lead encephalopathy and severely symptomatic lead poisoning.
• Mildly symptomatic/asymptomatic lead poisoning (lead levels >70 µg/dL or 3.38 µmol/L).
• Second-line chelation when succimer is unavailable or poorly tolerated.
• Other heavy metal poisonings (efficacy uncertain).

Contraindications

• Relative: Anuric renal failure.

Mechanism of Action

• Binds divalent and trivalent metals; calcium in EDTA is displaced, forming a stable, water-soluble chelate that is excreted in urine.

Pharmacokinetics

• Administration: Only IV due to incomplete oral absorption.
• Distribution: Limited to extracellular fluid.
• Excretion: Renal, dependent on glomerular filtration; half-life 20–60 minutes with normal renal function.

Administration

Lead Encephalopathy

• Critical care management: Start with dimercaprol (BAL) 4 mg/kg IM every 4 hours for 5 days.
• EDTA infusion: 50–75 mg/kg diluted in 500 mL saline or 5% dextrose, infused over 24 hours starting 4 hours after dimercaprol.
• Duration: Usually up to 5 days, with a 2–4 day break before considering a new course.
• Ongoing therapy: Continue until clinical stability is achieved. Switch to oral succimer if the patient stabilizes and tolerates it.

Symptomatic Lead Poisoning Without Encephalopathy

• Initial management: Dimercaprol 3 mg/kg IM every 4 hours for 5 days.
• EDTA infusion: 25–50 mg/kg in 500 mL saline or 5% dextrose over 24 hours.
• Duration: Typically 5 days, with breaks as in encephalopathy cases.

Adverse Drug Reactions and Management

Local Reactions:

• Pain and thrombophlebitis from rapid IV administration; minimize by:
  • Using a dilute solution (<0.5%).
  • Infusing over >4 hours.

Systemic Reactions:

• Malaise, fatigue, thirst, fever, myalgias, dermatitis, headache, anorexia, urinary frequency, nasal congestion, hypotension, transaminase elevations, ECG changes.

Nephrotoxicity:

• Risk due to EDTA-metal complexes in acidic urine; reduced by:
  • Ensuring hydration and urine flow of 1–2 mL/kg/hour.
  • Limiting dose to 2 g/day (1 g in children).
  • No continuous therapy beyond 5 days.
  • Daily renal function monitoring.

Specific Considerations

• Pregnancy: Safety not established; use if clinically indicated.
• Paediatrics: Same doses as adults but may use smaller fluid volumes. Oral succimer preferred when possible.

Handy Tip

• Asymptomatic or minimally symptomatic patients should receive oral succimer over EDTA if tolerated.

Pitfall

• Risk of mistakenly administering dicobalt edetate (for cyanide poisoning) instead.

Controversies

• EDTA may mobilize lead from soft tissues to the CNS; thus, not used as sole therapy for lead levels >70 µg/dL (3.38 µmol/L).
• Uncertainty about EDTA’s ability to reverse neurobehavioural effects of lead poisoning.
• Debate over using diagnostic EDTA chelation tests for total body lead assessment.