Concentration of ethambutol in cerebrospinal fluid in man as a function of the non-protein-bound drug fraction in serum.

Abstract

Using a chemical assay method, which had been confirmed by chromatography, the concentration of ethambutol in CSF and serum was determined in 13 patients. Ethambutol entered the CSF, even at low serum concentrations. For serum levels greater than 1 µg/ml, a linear correlation was found between the serum and CSF concentrations. In order to reach therapeutic levels in CSF (more than 1 µg/ml) the serum concentration should be at least 2 µg/ml, corresponding to a daily dose of about 20–30 mg/kg. The serum protein binding of ethambutol varied from 39.3% at a serum level of 0.61 µg/ml, to 8.3% at a serum level of 4.82 µg/ml.