Dose-dependent kinetics of ethotoin in man.

1. A gas-chromatographic assay for the anticonvulsant drug ethotoin in plasma has been used to establish a kinetic basis for therapy in eight newly diagnosed epileptic patients. 2. Only a small fraction of ethotoin was excreted unchanged. Elimination curves were only rectilinear below a plasma concentration of 8 mg/l. During constant medication plasma concentrations tended to decrease in the first week. Steady-state plasma levels varied considerably between individuals. For all patients the plasma concentration/dose ratio increased with increasing dose. 3. Most of the results point to dose-dependent elimination kinetics in the therapeutic range and parallel what is known for phenytoin. Control of therapy by measurement of plasma levels of ethotoin is accordingly advocated.