Nonstereoselective disposition of ethosuximide in humans.

The total concentration of ethosuximide varied between 80 and 770 mumol/L in plasma samples obtained from 33 patients on long-term treatment with the racemic drug. The ratios between the two enantiomers measured by chiral gas chromatography in the same samples were close to unity (mean +/- SD = 1.06 +/- 0.14; range = 0.76-1.39). This suggests that the disposition of ethosuximide in humans is not stereoselective and that the measurement of total concentrations of ethosuximide is sufficient for therapeutic monitoring.