Iron poisoning

•Commonest in childhood and accidental

•Normal concn is 50-165 micrograms/dl

•10 to 20 % of the 10 to 20 mg recommended dietary iron is absorbed

Mechanism of toxicity

•Serum binds 3 to 4 micrograms/ml of iron

•Excess amount of iron absorbed is carried unbound in the blood and causes tissue damage in the gastro intestinal tract (GIT), in the liver and the kidneys

•Soluble ferric and ferrous salts also corrode the stomach and small intestines causing ulcers and haemorrhage

Signs and symptoms

•Principal manifestations: vomiting, diarrhoea and circulatory collapse

•Acute poisoning: Lethargy, nausea, haematemesis, hypotension, acidosis, vomiting and diarrhoea, tarry stools and a fast weak pulse. Occur within half an hour to one hour of ingestion of the salt

•Symptoms may resolve within an hr and resume after 24 hrs

•May then return and cause: pulmonary oedema, anuria, shock, convulsions, hyperthermia & coma

•Injected Fe: Fever, tachycardia, skin rash, back pain and anaphylaxis

Laboratory findings

•Increased haemoglobin

•Raised red blood cell (RBC) count

•Blood in stool (melaena)

Emeregncy management

•Induce emesis using ipecac syrup

•Perform a gastric lavage using a fluid containing desferrioxamine (2 grams per litre of water) as one of the components

•Leave 10 grams of desferrioxamine in the stomach in either 100ml of water or in a solution of sodium bicarbonate

•Establish the airways and maintain respiration

•Administer saline or dextrose to correct electrolyte imbalance and dehydration

•Maintain blood pressure by cautiously transfusing blood or plasma

Antidote

•Desferrioxamine a chelating agent binds ferric iron (Fe3+) and forms Fe3+ - desferrioxamine complex

•Complex less toxic than free iron and more easily excreted

•Asymptomatic patients: 90mg/kg to 1 gram of desferrioxamine (I.M)

•Symptomatic patients or patients whose serum levels exceed 63 micro moles per litre of iron, give desferrioxamine (I.V) 15mg/kg/hour to a max of 80mg/kg in 24hrs

•Monitor BP during administration, decrease rate if BP falls

•Note: single dose sh’d not exceed 1g, 24hr dose sh’d not exceed 6g

•Toxic to patients with renal disease or anuria

•Administered until symptoms resolve for 24hrs

GENERAL MEASURES

•Treat shock;

•Treat the acidosis with oxygen (O2) or sodium bicarbonate 5 grams orally. In severe acidosis give sodium bicarbonate intravenously (8.4% by slow intravenous injection; 1.26% by continuous intravenous infusion);

•Maintain adequate intravenous and tissue perfusion by giving blood or fluid intravenously;

•Treat any infections with antibiotics;

•Maintain a high urine output of 1ml/kg/hour;

•Gastrectomy might be needed to remove a bolus of iron tablets

Prevention

•Dispense iron in child resistant containers

•Keep iron preparations out of reach of children

Chronic iron poisoning

•May occur in aplastic and other refractory anaemia as a result of repeated transfusions

•Parenteral Fe administration in over dosage causes exogenous haemosiderosis with damage to the liver and pancreas

•Metabolic absorption defect causing haemochromatosis

Treatment

•Venesection (phlebotomy): haemochromatosis and in patients who have received multiple transfusions and whose bone marrows have recovered;

•Desferrioxamine mesylate: Long term treatment of chronic iron exposure. Given by subcutaneous infusion in a dose of 20 to 40 mg/kg over 8 to 12 hours on 3 to 7 nights each week. Up to  2 grams/unit of desferrioxamine can be given through the intravenous line at the time of blood transfusion;

•Vitamin C in a dose of 200mg (100mg for infants) daily and given separately from food enhances iron excretion by desferrioxamine