Isoniazid Overdose

Acute ingestion of as little as 1.5–2.0 g can cause toxicity

Severe poisoning is likely to occur after ingestion of more than 80–100 mg/kg

May cause hepatitis with long-term use

Confusion, slurred speech, and seizures may occur abruptly after acute overdose

Severe lactic acidosis—disproportional to the severity of seizures—is probably due to inhibited metabolism of lactate

Peripheral neuropathy and acute hepatitis may occur with long-term use

Diagnosis is based on a history of ingestion and the presence of severe acidosis associated with seizures

Isoniazid is not usually included in routine toxicology screening, and serum levels are not readily available

Administer activated charcoal after large recent ingestion but with caution because of the risk of abrupt onset of seizures

Seizures may require higher than usual doses of benzodiazepines (eg, lorazepam, 3–5 mg intravenously)

Pyridoxine (vitamin B₆)

• A specific antagonist of the acute toxic effects

• Usually successful in controlling seizures that do not respond to benzodiazepines

• Give 5 g over 1–2 minutes intravenously or if the amount ingested is known, give a gram-for-gram equivalent amount of pyridoxine