Isoniazid overdose: pharmacokinetics and effects of oral charcoal in treatment

The pharmacokinetics of isoniazid following overdose in two patients is described. One patient was treated with haemodialysis for seizures and persistent coma without obvious immediate clinical improvement. In addition, three volunteer subjects were given isoniazid orally on two separate occasions. Isoniazid elimination pharmacokinetics were determined with and without concominant charcoal. Oral activated charcoal totally prevented the absorption of isoniazid. Current recommendations for treatment of isoniazid overdoses include intravenous pyridoxine (one gram IV pyridoxine for each gram of ingested isoniazid), intravenous diazepam or phenobarbital for continued seizures, and gastric decontamination with lavage and activated charcoal (1 g/kg). Extraordinary measures such as early haemodialysis and haemoperfusion should be reserved for those patients with persistent coma or refractory seizures.