Taking too much isoniazid (INH) can result in a toxic reaction which can be lethal.
Toxic doses of isoniazid:
(1) A toxic dose may be as little as 1.5 g.
(2) A dose >= 30 mg/kg can result in seizures.
(3) A dose >= 80 mg/kg can be fatal.
Clinical features of isonizid overdosage:
(1) nausea and vomiting
(2) slurred speech
(3) dizziness
(4) tachycardia
(5) urinary retention
(6) altered mental status including stupor and coma
(7) recurrent grand mal seizures, which often are resistant to standard anticonvulsant therapy
(8) fever
(09) skin rash
(10) ataxia
(11) peripheral neuritis
(12) respiratory failure
Laboratory findings:
(1) severe metabolic acidosis with elevated serum lactic acid
(2) increased anion gap
(3) hyperglycemia
(4) hypokalemia
(5) elevated blood levels of isoniazid. The blood level is not useful in management but can confirm the diagnosis if it is in doubt.
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Specialty: Toxicology, Emergency Medicine, Critical Care, Infectious Diseases
