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Chapter: Modern Medical Toxicology: Corrosive(Caustic) Poisons: Organic Acids

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Formic Acid - Corrosive(Caustic) Poisons

Aminic acid; Formylic acid; Hydrogen carboxylic acid; Methanoic acid.

Formic Acid

Synonyms

Aminic acid; Formylic acid; Hydrogen carboxylic acid; Methanoic acid.

Physical Appearance

Colourless liquid with a pungent, penetrating odour.

Uses/Sources

·      Formic acid is a natural constituent of some fruits (apples, pears, plums, apricots), nuts, and dairy products. Some wines may contain formic acid.

·      Formic acid is an important toxic metabolite produced in methanol poisoning.

Industrial uses

·      Component of descaling and stain-removing agents

·      Reducing agent in wool/textile dyeing

·      Leather tanning, plumping and dehairing product for hides

·      Coagulation of latex rubber Electroplating

Agricultural uses

·      Animal feed additive

·      Food preservative, flavour enhancer: Formic acid has been used as a food additive in small amounts (e.g. 0.1 to 6 ppm) in ice cream, ices, candy, and baked goods.

Therapeutic uses

·      Removal of tattoosComponent in some external preparations for the treat-ment of musculoskeletal and joint disorders.

Usual Fatal Dose

Ingestions of less than 10 grams in children have resulted in oropharyngeal burns; no deaths were reported. Solutions of 10% or less are generally considered noncorrosive. Ingestions between 5 and 30 grams may result in symptomatic burns of the gastrointestinal tract and haematemesis, but death is unusual. Ingestions between 45 to 200 grams often result in death within the first 36 hours post-ingestion.

Toxicokinetics

Formic acid is readily absorbed from the GI tract.

Mode of Action

·     Coagulative necrosis type of corrosive action on the GI mucosa.

·     Damages clotting factors and causes haemolysis leading to acute renal failure.

·     At the cellular level, it has an inhibitory action on aerobic glycolysis with consequent diminution of ATP synthesis.

Clinical Features

·      GIT: Burning pain, salivation, vomiting, mucosal corrosionand ulceration, haematemesis.

·      CNS: Drowsiness, weakness, coma. Pupils are dilated.

·      CVS: Tachy/bradycardia, hyper/hypotension.

·      Blood: Haemolysis, DIC.

·      RS: Acute respiratory distress, aspiration pneumonitis,“shock lung”.

·      Metabolic: Acidosis, acute tubular necrosis, shock, anddeath.

·      Skin: Erythema, blisters.

 

Treatment

·      First-aid : Immediate dilution, by administering milk.

·      Induction of emesis, gastric lavage, and use of activated charcoal are all contraindicated.

·      High dose folinic acid (1 ml/kg IV bolus, followed by 6 doses of 1 mg/kg IV at 4 hourly intervals) is recommended by some investigators, since it is supposed to enhance formate degrada-tion by the liver.

·      Supportive measures, with particular emphasis on dialysis, exchange transfusion, intubation, ventilatory support, and correction of metabolic acidosis and renal failure.

Autopsy Features

Blackish corrosion of GI mucosa, pulmonary oedema.

Forensic Issues

·     Accidental and suicidal poisoning with formic acid is relatively common in those areas where the chemical is easily available, for instance in Kerala where manufacturing rubber is a major industry.

Methanol poisoning, is associated with formic acid toxicity, since it is metabolised in the body to produce formaldehyde and formic acid.

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