Antidote: pyridoxine
Intravenous pyridoxine (vitamin B6) is indicated for acute isoniazid poisoning complicated by seizures or metabolic acidosis.
For adults and children who ingested 5 g or less of isoniazid, and have seizures or metabolic acidosis, use:
pyridoxine at a dose equivalent to the amount of isoniazid ingested, up to 5 g (eg for a 4 g ingestion of isoniazid, give 4 g of pyridoxine), by intravenous infusion at a rate of 500 mg/minute. Repeat the dose after 30 minutes if seizures or metabolic acidosis do not resolve. If seizures stop, infuse the rest of the dose over 4 hours1. isoniazid poisoning
For adults and children who ingested an unknown dose or more than 5 g of isoniazid, and have seizures or metabolic acidosis, use:
pyridoxine 5 g by intravenous infusion at a rate of 500 mg/minute. Repeat the dose after 30 minutes if seizures or metabolic acidosis do not resolve. If seizures stop, infuse the rest of the dose over 4 hours1.
Pyridoxine clearance is increased during haemodialysis; repeat doses or higher doses of pyridoxine may be required in patients receiving haemodialysis—discuss with a clinical toxicologist.
If intravenous pyridoxine is not available or there is inadequate supply, oral pyridoxine can also be given in a dose equivalent to the amount of isoniazid ingested; however, administration of activated charcoal will reduce pyridoxine bioavailability. Oral pyridoxine is available in a range of strengths.