6.3 Biological half-life by route of exposure
The serum half-life in therapeutic doses is 3 hours,
increasing in renal failure, as 80% is excreted renally
(Gilman et al., 1990).
In 6 healthy subjects given a single dose of ethambutol 15
mg/kg bodyweight as an aqueous solution and as a commercial
tablet preparation the apparent mean elimination half-life
was 4.78 and 4.06 hours respectively, for plasma
concentration measured up to 12 hours after administration.
It was increased to about 10 hours for 24 to 72 hour
samplings. The serum levels of ethambutol falls to
undetectable levels by 24 hours after the last dose, except
in some patients with abnormal renal function.