Isoniazid is one of the most commonly used antituberculosis drug. Acute into xication is characterized by repetitious convulsions, high anion gap metabolic a cidosis and coma. The basis of theraphy consists of parental pyridoxine admi nistration in a dose equivalent to that of isoniazid ingested. Here we present a case of seizure and metabolic acidosis due to only renal adjustment dosage of Isoniazid in an elderly woman.