Symptoms: Toxic symptoms include vomiting, abdominal pain, hypotension and sweating. The most serious adverse effect of acute overdose of paracetamol is a dose-dependent, potentially fatal hepatic necrosis. Clinical and laboratory evidence of hepatotoxicity may be delayed for up to one week. Major manifestations of liver failure such as jaundice, hypoglycemia and metabolic acidosis may take at least 3 days to develop.
Treatment: In cases of overdose, methods of reducing the absorption of ingested drug are important. Gastric lavage is essential even if several hours have elapsed. Prompt administration of 50 g activated charcoal and 500 ml iced mannitol 20% by mouth, may reduce absorption. If the history suggests that 15 g Paracetamol or more has been ingested, administer one of the following antidotes: Acetylcysteine 20% i.v: Administer intravenously, 20% acetylcysteine (Parvolex, Glaxo) immediately without waiting for positive urine test or plasma level results: initial dose of 150 mg/kg over 15 minutes, followed by continuous infusion of 50 mg/kg in 500 mL 5% glucose/dextrose over 4 hours and 100 mg/kg in 1L 5% glucose/dextrose over 16 hours.
Oral Methionine: 2.5 g immediately followed by three further doses of 2.5 g at four hourly intervals. For a 3-year old child, 1 g methionine every four hours for four doses has been used.
Oral Acetylcysteine 5%: 140 mg/kg as a loading dose, then 70 mg/kg every 4 hours for a total of 17 maintenance doses. If more than ten hours have elapsed since the overdosage was taken, the antidote may be in ineffective.