Isoniazid Poisoning

Aka: Isoniazid Poisoning, Isoniazid Overdose, Isoniazid Toxicity

1. See Also
   1. Isoniazid
2. Pharmacokinetics
   1. Absorption rapid
   2. Peak levels: 1 to 2 hours
   3. Toxic Levels: >20 mg/kg
3. Mechanism: Toxicity
   1. Pyridoxine Deficiency
   2. Glutamic Dehydrogenase inhibition
      1. Blocks conversion of glutamate to GABA
      2. Results in GABA deficiency
4. Symptoms
   1. Nausea
   2. Vomiting
   3. Altered Mental Status
   4. Ataxia
   5. Seizures or Status Epilepticus
      1. Ingestions >20 mg/kg
   6. Rhabdomyolysis
5. Labs
   1. See Unknown Ingestion for broad based lab evaluation after ingestion
   2. Labs in isolated Isoniazid ingestion
      1. Bedside Glucose
      2. Basic metabolic profile
      3. Creatinine Phosphokinase
6. Imaging
   1. CT Head
      1. Consider in unknown cause of Altered Level of Consciousness or Status Epilepticus
7. Diagnostics
   1. Electroencephalogram (EEG) monitoring
      1. Indicated in persistant or recurrent Seizures
8. Management
   1. Decontamination
      1. Activated Charcoal 1 g/kg if presenting within one hour of ingestion, and airway protected
      2. Consider Hemodialysis if started early in large ingestions
   2. Pyridoxine
      1. Give same dose of Pyridoxine of the Isoniazid ingestion if known OR
      2. Pyridoxine 70 mg/kg (up to 5 g) IV over 3 to 5 minutes
      3. May repeat dosing for recurrent Seizures
   3. Seizures
      1. See Status Epilepticus
      2. Lorazepam 0.5 to 1 mg/kg (up to 2 mg/dose) as needed
   4. Disposition
      1. Observe or admit all patients with recurrent Seizures or persistent Altered Mental Status
      2. May discharge after 4 to 6 hours following ingestion if asymptomatic
9. References
   1. Tomaszewski (2018) Crit Dec Emerg Med 32(7):28