A seven-year-old boy ingested 3,000 mg (125 mg/kg) of isoniazid. Initial blood levels of isoniazid were 250 micrograms/mL approximately six hours after ingestion. Despite IV treatment in the emergency department with 3,000 mg pyridoxine and a repeat of the same antidote one hour later in the intensive care unit, the high isoniazid blood levels and persistent metabolic acidosis and coma prompted a decision to increase drug clearance by hemodialysis. Clearance data confirmed the effectiveness of hemodialysis in removing the poison, and the clinical response was dramatic.