Saturable metabolic pathways for ethotoin in man.

1. The urinary excretion pattern of ethotoin and five metabolites were examined in three patients receiving continuous treatment with ethotoin at two dose levels, in order to investigate the mechanism behind the dose-dependent kinetics of this anticonvulsant drug. 2. The results suggest a partial saturation in the dealkylation process at high dose levels in three patients. 3. A rough approximation of the Michaelis-Menten constants for different enzymatic processes was attempted. On the basis of the results obtained, the p-hydroxylation may be a saturable process. 4. The dose-dependent kinetics of ethotoin in man seem to be explicable by the existence of partly saturable enzymatic pathways.