Isoniazid Poisoning

Description

Diagnostic criteria

General and supportive measures

Medicine treatment

Referral

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ICD-10 code: T37.1

DESCRIPTION

INH interferes with pyridoxine and niacin metabolism, leading to impaired synthesis of gamma aminobutyric acid (GABA).  Acute poisoning, which may follow intentional or accidental ingestions, may be severe.

DIAGNOSTIC CRITERIA

Clinical

Triad of refractory seizures, metabolic acidosis and coma within 2-3 hours of ingestion. Hyperthermia and rhabdomyolysis can develop after prolonged seizure activity.

Investigations

• Metabolic acidosis - high anion gap due to lactate accumulation.

GENERAL AND SUPPORTIVE MEASURES

• Respiratory and circulatory support

MEDICINE TREATMENT

• Activated charcoal, See: Poisoning, Treatment.
• For seizures:
  • Pyridoxine is the primary treatment of seizures and coma, which once controlled, should help resolve metabolic acidosis.
    • Asymptomatic patients presenting within 2 hours, give an initial prophylactic dose of 70 mg/kg of oral pyridoxine up to a maximum dose of 5 g.
    • Symptomatic patients with significant symptoms or seizures: replace INH with pyridoxine gram-for-gram, up to a maximum of 5 g.
    • Oral pyridoxine 25 mg tablets can be crushed and given with fluids via nasogastric tube.
    • If seizures recur, repeated doses of pyridoxine may be given up to a maximum daily dose of 15-30 g.

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Note:  
Benzodiazepines and phenobarbitone may be used to control seizures (whilst pyridoxine is being prepared/given). Phenytoin should be avoided (due to potential cardiotoxicity).

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LoE III⁴

• Metabolic acidosis should improve with seizure control, but additional sodium bicarbonate may be required.

REFERRAL

• Refractory seizures

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Standard Treatment Guidelines and Essential Medicines List for South Africa, Hospital Level, Paediatrics, 2023 Edition

Chapter 18: Poisoning,  18.1 Poisoning,  18.1.17 Isoniazid Poisoning