A neurological examination may show abnormalities. Blood levels of the medication may show toxic levels. Normal blood levels of certain drugs may be toxic in elderly or other highly susceptible persons.
Goetz, CG. Textbook of Clinical Neurology. 2nd ed. St. Louis, Mo: WB Saunders; 2003: 1235.
Goldman L, Ausiello D. Cecil Textbook of Medicine. 22nd ed. Philadelphia, Pa: WB Saunders; 2004:2385.