Chelating agents are drugs that form complexes with heavy metals to facilitate their removal from the body. They work by binding metals like lead, arsenic, and mercury to create non-toxic, water-soluble complexes that can be excreted in urine. Common chelating agents include dimercaprol, dimercaptosuccinic acid, dimercaptopropane sulfonic acid, disodium edetate, penicillamine, and desferrioxamine. Each agent has affinity for specific metals and is used to treat poisoning from those metals. The ideal chelating agent rapidly forms complexes that are non-toxic and easily excreted to safely eliminate metals from the body.

1. CHELATING
AGENTS
By:
Dr Rishitha Krishna

2. CHELATING AGENTS
 These are the drugs used to prevent heavy metal
poisoning.
 Chelation: The process of an equilibrium reaction between
a metal ion and complexing agent which produces a
stable, non-ionized, non-toxic and water soluble complex
which can be eliminated easily.
 These compounds are usually flexible organic molecules
which can incorporate metal ions into their molecular
structure by means of chemical groups called ligands.

3. MECHANISM OF ACTION
Drugs + metallic ions
Non toxic water soluble complex
Eliminated by the kidneys

4. IDEAL CHELATING AGENT
 More affinity for metal than endogenous ligands.
 High solubility in water.
 Resistance to bio transformation.
 Form non toxic complexes with toxic metals.
 Accelerate mobilization and/or removal of the metals.
 Cheap and easy to administrate.
 Easy excretion of chelating complex.

5. COMMON CHELATING AGENTS USED
 Dimercaprol (BAL)
 Dimercaptosuccinic Acid (DMSA)
 Dimercaptopropane Sulfonic Acid (DMPS)
 Disodium edetate (EDTA)
 Calcium disodium edetate
 Penicillamine
 Desferrioxamine & Deferiprone

6. EDTA
Dimercaprol
(BAL)
Dimercaptosuccinic
Acid (DMSA)
Penicillamine
Desferrioxamine &
Deferiprone
Lead
Arsenic, Copper,
Mercury
Lead, Arsenic,
Mercury
Copper, Mercury,
Lead
Iron

7. DIMERCAPROL (BAL)
 Synthesised during the World War II by Britisher’s as an antidote to
arsenic war gas Lewisite.
 oily, pungent smelling, viscous fluid.
 Route of administration – i.m in oil (arachis oil)
 SH ligands of dimercaprol compete with – SH groups of enzymes
for heavy metal.
 Excess of dimercaprol should be maintained in plasma.
 Dimercaprol-metal complex is stable and excreted in urine.

8. USES
For the treatment of arsenic and mercury
poisoning.
As an adjuvant to calcium disodium edetate in
lead poisoning.
As an adjuvant to penicillamine in copper
poisoning and in Wilson’s disease.
Contraindicated in iron and cadmium poisoning.

9. DMPS (UNITHIOL)
Dimercaprol analogue
 water soluble, less toxic.
 Can be administrated orally as well as IV.
 Used for severe acute poisoning by mercury and
arsenic.
 Also effective in the treatment of lead poisoning.
 Adverse effects are low, except for mild self-limiting
urticaria.

10. DISODIUM EDETATE (EDTA)
It is a disodium salt of EDTA.
Potent chelator of calcium.
Causes tetany on IV injection (but not on slow
infusion)
Can be used for emergency control of
hypercalcemia (rare) 50 mg per kg IV over 2-4
hours.

11. CALCIUM DISODIUM EDETATE
 Calcium chelator of Disodium edetate.
 Has a high affinity for lead.
 Most important use in lead poisoning.
 Poorly absorbed from GI.
 IM is very painful – IV preferred.
 Not metabolised.
 Excreted by glomerular filtration and tubular secretion.

12. PENICILLAMINE
Dimethyl cysteine
 water soluble degradation product of penicillin.
 D-isomer is used – relatively non toxic compared to I-
isomer.
 Easily absorbed in GIT.
 Little metabolised, excreted in urine and faeces.
 It has strong copper chelating property and was used in
1956 for Wilson’s disease.
 It selectively chelates copper, mercury, lead and zinc.

13. USES
Wilson’s Disease (Hepato-lenticular degeneration)
 Copper/Mercury poisoning.
 Adjuvant to calcium disodium edetate in lead poisoning
but DMSA is preferred.
 Cystinuria and cysteine stones.
 Scleroderma – benefits by increasing the soluble collagen.
 Used as a Disease Modifying Drug in Rheumatoid Arthiritis
but now replaced by safer drug.

14. DESFERRIOXAMINE
 Ferrioxamine obtained from actinomycete, long chain iron
containing complex.
 Chemical removal of iron from it yields desferrioxamine.
 1 gm is capable of chelating 85 mg of elemental iron.
 Low affinity for calcium.
 Parenterally – partially metabolised, rapidly excreted in
urine.
 Acute iron poisoning : mostly in children, important and
life saving.

15. DEFERIPRONE
Orally active.
Used in transfusion siderosis.
Also indicated in iron poisoning and iron load in
liver cirrhosis.

16. CONCLUSION
Primary goals of chelating therapy:
To reduce metal retention.
To decrease morbidity and mortality.
To prevent complications.
Administer less toxic chelator when possible.