Pediatric emergency medicine trisk 3091 3091
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include hepatic dysfunction and interactions with foods such as those containing
tyramine. However, its greatest toxicity appears after acute single ingestions of
more than 20 mg/kg in children or more than 1.5 g in an adult.
INH’s mechanism of toxicity involves its potent reversal of the biologic
activity of vitamin B6 (pyridoxine). This action, as well as other effects on the
synthesis of catecholamines and the neurotransmitter GABA, provides an
explanation for the epileptogenic toxicity of the drug. INH also prevents hepatic
conversion of lactate to pyruvate.
Clinical Considerations. In overdose, the hallmark of INH poisoning is the triad
of seizures, metabolic acidosis, and coma. Seizures induced by INH are typically
generalized and appear to have a rhythmic recurrence. They are generally difficult
to treat and patients usually remain comatose between seizures. The metabolic
acidosis of INH can be severe; pH values of as low as 6.4 have been reported. As
such, INH is on the list of substances associated with the development of high
anion gap metabolic acidosis (see MUDPILES mnemonic). Of all these drugs,
only INH possesses seizures as a prominent characteristic. Interestingly, in animal
models of INH poisoning, metabolic acidosis does not occur if seizures are
prevented through paralysis. Finally, the coma of INH intoxication can be severe
and prolonged.
Because of the striking clinical picture of INH poisoning, diagnosis is often
easily made on the basis of demographic characteristics (particularly common in
patients from Southeast Asia or history of incarceration) and clinical
manifestations. INH is not usually detected on routine toxicology laboratory
screens, and serum concentrations are of little value in acute management.
Laboratory tests important in initial assessment include arterial blood gas levels,
electrolytes level, liver function tests, creatine kinase level, and urinalysis.
Management. Management of INH intoxication begins with advanced life
support. Because of seizures and coma, airway protection and ventilation are
typically necessary. Initiate cardiac monitoring for the development of cardiac
arrhythmias (resulting from severe metabolic acidosis).
Activated charcoal may also be considered if it can be given safely.
Theoretically, giving multiple doses of activated charcoal to enhance
postabsorptive elimination of INH may be advantageous, but this approach must
be weighed against the risk of seizure.
Pharmacologic treatment for INH intoxication includes sodium bicarbonate,
anticonvulsants, and pyridoxine. Sodium bicarbonate is provided as needed to
