CHELATORS AND HEAVY METALS

TERMSDefinition

Chelating agentA molecule with two or more electronegative groups that can form stable coordinate complexs with multivalent cationic metal atoms

erethismSyndrome resulting from mercury poisoning characterized by INSOMIA, MEMORY LOSS, EXCITABILITY, and DELIRIUM

picaIngestion of nonfood substances; pica also refers to ingestion of lead-based paint fragments by small children

PlumbismRange of toxin syndromes due to chronic lead poisoning that may vary as a function of blood or tissue levels and patient age

CHELATORSA. Dimercaprol: bidentate chelatora. Clinical use: for acute arsenic and mercury poisoning. For lead poisoning in conjunction with edentate. Given parenterallyb. Toxicity: very lipophilic, readily enters cells. Toxicity includes transient hypertension, tachycardia, headache, nausea, vomiting, paresthesia, and fever.

B. Succimer: bidentate chelatora. Clinical use: for lead toxicity. For arsenic, mercury poisoningb. Toxicity: GIT distress, CNS effect, skin rash, elevation of liver enzymes. Should not be administered with other chelating drugs

C. Penicillamine: bidentate chelatora. Clinical use: for treatment of copper poisoning and Wilsons disease. For gold, arsenic, lead intoxication, rheumatoid arthritis.b. Toxicity: nephrotoxic

D. Edentate (EDTA): polydentate chelatora. Clinical use: for lead poisoning. Given as calcium disodium saltb. Toxicity: nephrotoxic. Risk can be reduced by adequate hydration and restricting treatment to 5 days

E. Deferoxamine: polydentate chelator. Competes with heme in hemoglobin ad cytochromea. Clinical use: for acute iron intoxicationb. Toxicity: skin reactions, neurotoxic, hepatic and renal dysfunction.TOXICOLOGY OF HEAVY METALSA. Lead: no useful purpose in the body. Present in air and water.a. Acute lead poisoning: primary signs are acute abdominal colic and CN changes. In children, may take form of acute encephalopathy.b. Chronic lead poisoning (plumbism). Signs include peripheral neuropathy, anorexia, tremor, GIT symptoms. Treatment includes removal from the sources of exposure and chelation therapy usually with edentate, demercaprol or penicillaminec. Organic lead poisoing: due tetraethyl lead or tetramethyl lead antinonck gasoline additives. Primary signs are in the CNS that includes hallucinations, headache, irritability, convulsions, and coma. Treatment consists of decontamination and seizure control.

B. Arsenic: released during burning of coal. Known human carcinogen.a. Acute arsenic poisoning: results in severe GIT discomfort, vomiting, rice-water stools. A sweet, garlicky odor may be detected in the breath and stools. Treatment consists of supportive therapy to replace water and electrolytes and chelation therapy with dimercaprol.b. Chronic arsenic poisoning: manifested by skin changes, hair loss, bone marrow depression and anemia, and chronic nausea and GIT disturbances. Treatment includes dimercaprol.c. Arsine gas: used in semiconductor industry. Signs include massive hemolysis. Treatment is supportive.

C. Mercurya. Acute mercury poisoning: occurs through inhalation of inorganic elemental mercury. Causes chest pain, shortness of breath, nausea, and vomiting, kidney damage, CNS damage. Treatment includes dimercaprol.b. Chronic mercury poisoning: syndrome involving the gums ad teeth, GIT disturbances, and neurologic and behavioral changes. Treatment with penicillamine and dimercaprol.c. Organic mercury poisoning

D. Iron: Acute poisoning from ingestion of ferrous sulfate tablets occurs in children. Initial symptoms include vomiting, GIT bleeding, lethargy, gray cyanosis. Followed by signs of severe GIT necrosis, jaundice, seizures, and coma. Deferoxamine is the chelating agent of choice.

metalForm of entering Route of absorptionTarget organs for toxicityTreatment

LeadInorganic lead oxides and salts

Tetraethyl leadGIT, respiratory, skin

Skin, GITHematopoietic system, CNS, kidneys

CNSDimercaprol, edentate, penicillamin, succimer

Seizure control, supportive

ArsenicInorganic arsenic salts

Arsine gasAll mucosal surfaces

InhalationCapillaries, GIT, hematopoietic

ErythrocytesDimercaprol, succimer, penicillamine

Supportive

MercuryElemental

Inorganic salts

Organic mercurialsInhalation

GIT

GITCNS, kidneys

Kidneys, GIT

CNSDimercaprol

Penicillamine, dimercaprol

Supportive

IronFerrous sulfateGITGIT, CNS, blooddeferoxamine