Isoniazid (INH) Poisoning — Management Pathway

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Suspect INH poisoning?
   Refractory seizures + metabolic acidosis — suspect INH poisoning? (A TB drug; depletes pyridoxine (B6) → reduced GABA → seizures. Toxic from ≥1.5 g, seizures >30 mg/kg. Onset 30 min–2 h. Classic triad: refractory seizures unresponsive to usual anticonvulsants + high-anion-gap metabolic acidosis + coma; refractory seizures + acidosis should prompt suspicion of INH (especially TB patients / those with drug access).)
   • Seizures/coma (acute neurotoxicity) → Seizures/coma → pyridoxine antidote
   • Ingestion history, no seizures yet → Ingestion history · pyridoxine ready, observe
2. [End] Ingestion history · pyridoxine ready, observe
   Ingestion history, no seizures yet: airway/monitoring, check blood gas and electrolytes; activated charcoal if early (<1 h, airway protected); have an adequate dose of pyridoxine ready at the bedside (a hospital emergency stock of ~8 g); observe closely and give pyridoxine the moment a seizure occurs.
3. [End] Seizures/coma → pyridoxine antidote
   Seizures/coma (acute neurotoxicity): airway support, benzodiazepines for seizures; specific antidote — IV pyridoxine (vitamin B6) gram-for-gram with the ingested INH (if the amount is known; max first dose 5 g), or 70 mg/kg empirically if the amount is unknown (max 5 g), repeatable, rapidly terminating seizures/correcting acidosis; phenytoin is ineffective and used with caution (INH inhibits its metabolism); correct acidosis, fluids; large ingestion/renal failure may need hemodialysis; toxicology consult.

Source guidelines & references

• Isoniazid poisoning (StatPearls; AAFP; Medscape)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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