Concentrations of ethambutol in the cerebrospinal fluid after oral administration

Abstract

After administration of a single dose of 25 mg./kg. of body weight, ethambutol levels were determined in the serum and CSF of healthy subjects and patients with active tuberculous meningitis. Determinations were made 3, 6, 9, 12, 15 and 24 hours after ingestion. At 3 hours, an average of 4·1 μg./ml. was found in the serum of the normal individuals and 4·9 μg./ml. in the serum of patients with meningitis. The levels fell to zero 24 hours after ingestion. Ethambutol penetrated the CSF in very few normal subjects; but in patients with meningitis the mean levels were 0·48 μg./ml. at 3 hours, 0·35 μg./ml. at 6 hours, 0·12 μg./ml. at 9 hours, 0·18 μg./ml. at 12 hours and 0·07 μg./ml. at 15 hours and 24 hours. But at each interval (except at 15 hours) no ethambutol was detected in some of the cases. The fact that ethambutol penetrates the meningeal barrier in patients with tuberculous meningitis means that it will be active against lesions located there. It is concluded that ethambutol is an effective drug in the treatment of tuberculous meningitis.