Sodium Calcium Edetate

Why this drug is interesting

Sodium calcium edetate is the oldest of the lead chelators still in routine use, and it remains the agent with the most clinical experience behind it in the sickest patients. It is also the one with a genuinely dangerous namesake, and the one whose supply in the UK is least reliable.

Pharmacology

Mechanism

The molecule is EDTA presented as its calcium disodium salt. Lead has a far higher affinity for the chelating cage than calcium does, so Pb²⁺ displaces the central Ca²⁺ and the resulting lead chelate is excreted renally.¹ Everything clinically important about the drug follows from that single exchange: it works because the calcium is there to be given away, and it is safe for the same reason.

Where the lead comes from

The primary source of lead mobilised by sodium calcium edetate is bone, with an additional contribution from kidney and liver.¹ Bone is where the body's lead burden actually resides, which is the theoretical argument for this agent — and also the reason chelation can be followed by rebound as bone stores redistribute.

Dosing

In the West Midlands Poisons Unit series, patients were chelated with intravenous sodium calcium edetate 75 mg/kg/day, or with oral succimer 30 mg/kg/day, according to stock.² Fifteen of sixty-three patients tested were chelated; the cohort ranged from 6 months to 78 years old.

Practical administration

Given by dilute intravenous infusion. Because the drug is renally excreted and nephrotoxic, urine output and renal function are monitored throughout, and adequate hydration matters. The specifics — dilution, infusion duration, whether to give it with or after dimercaprol in severe poisoning, and how to sequence courses — are exactly the questions NPIS exists to answer, and they vary with severity in a way this page cannot usefully reduce to a rule.

Safety

Nephrotoxicity

Trace element depletion

EDTA is not selective for lead. Both chelators deplete zinc and copper, but "the effect on zinc being significantly greater with sodium calcium edetate".¹ Skin lesions during treatment are unusual and, when they occur, have been attributed to zinc deficiency rather than to a drug allergy.¹ That attribution is worth knowing before a rash is called a reaction and the antidote is stopped.

Liver

A transient increase in hepatic transaminase activity has been reported with both agents, appearing more common with succimer, and neither has been associated with clinically significant hepatic toxicity.¹ A transaminase bump on treatment is expected rather than alarming.

Practical use in the ED

1. Say and write the full name — sodium calcium edetate. Never abbreviate it to "EDTA" on a prescription. The disodium salt is a different, dangerous drug.
2. Confirm the poisoning with a blood lead concentration, noting whether your laboratory reports µg/dL or µmol/L (1 µg/dL ≈ 0.048 µmol/L).
3. Call NPIS on 0344 892 0111 before choosing an agent. In encephalopathy, ask specifically about dimercaprol sequencing.
4. Check renal function before and during treatment, and keep the patient hydrated. The nephrotoxicity is dose-related and predictable.
5. Ask pharmacy early what is actually available. UK stock of both lead chelators is unreliable and has determined the choice of agent in a published UK outbreak.²
6. Remove the source of exposure, and consider who else has been exposed — 87 people were identified in the UK firing-range outbreak, including household contacts.²

Critical appraisal

Sodium calcium edetate's position rests on experience rather than on demonstrated superiority. The 2009 systematic comparison found only two clinical studies that had compared equimolar or similar doses of the two agents for urinary lead excretion, with no statistical difference between them and limitations in both; a further clinical study found comparable effects on blood lead concentrations at similar molar doses.¹

Read carefully, that sentence gives sodium calcium edetate the benefit of familiarity in the sickest patients and concedes everything else. The experimental picture is muddier still: study designs varied substantially in antidote dose, route, duration and lead dosing, and most compared an antidote against control rather than against the other antidote.¹ Anyone asserting that one of these drugs is clearly better than the other is going beyond the evidence.

The more actionable uncertainty in the UK is not pharmacological but logistical. An unlicensed antidote for an uncommon poisoning, held in few hospitals, chosen in a real outbreak by what happened to be in the cupboard, is a supply problem presenting as a clinical one — and the authors of that series say so explicitly.²

References

1. 1
   Bradberry S, Vale A. A comparison of sodium calcium edetate (edetate calcium disodium) and succimer (DMSA) in the treatment of inorganic lead poisoning. Clinical Toxicology (Philadelphia) 2009;47(9):841–858. PubMed 19852620. The backbone of this page. Source of the Ca²⁺/Pb²⁺ displacement mechanism, the bone-plus-kidney-and-liver origin of mobilised lead, the parenteral-route requirement, the absence of metabolism, extracellular distribution and <60 min half-life, the blood–brain barrier statement, the dose-related nephrotoxicity, the greater zinc depletion, the zinc-deficiency attribution of skin lesions, the transaminase comparison, the two-clinical-study finding and the quoted conclusion. Abstract read 6 September 2026.
2. 2
   Warsi A, Pucci MR, Bradberry SM, et al. Outbreak of lead poisoning from a civilian indoor firing range in the UK. Occupational and Environmental Medicine 2024;81(3):159–162. PubMed 38302418. West Midlands Poisons Unit. Source of the UK dose (IV sodium calcium edetate 75 mg/kg/day), the stock-availability finding, and the 87 exposed / 63 tested / 15 chelated figures and 6 months–78 years age range. Abstract read 6 September 2026.
3. 3
   electronic Medicines Compendium. medicines.org.uk/emc. Searched 6 September 2026 for edetate and for the historic UK brand Ledclair: both return a "No search results" page. No SmPC is published for sodium calcium edetate in the UK, so none can be cited. The emc is an industry-hosted compendium of published SmPCs and PILs, not the MHRA register — this establishes that no SmPC is published, rather than that no marketing authorisation exists anywhere.
4. 4
   National Poisons Information Service. TOXBASE · NPIS 0344 892 0111. Required. Sodium calcium edetate is unlicensed in the UK. Indication, dose, infusion practicalities, dimercaprol sequencing in encephalopathy and the endpoint are all NPIS decisions.