Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 38-38: Isoniazid Overdose + Key Features Download Section PDF Listen +++ ++ 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 + Clinical Findings Download Section PDF Listen +++ ++ 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 Download Section PDF Listen +++ ++ 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 + Treatment Download Section PDF Listen +++ ++ 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