Paramethadione and Metabolite Serum Levels in Humans after a Single Oral Paramethadione Dose

A GLC method was developed to determine quantitatively paramethadione and its major metabolite, 5-ethyl-5-methyl-2,4-oxazolidinedione, in serum. The method was reproducible and sensitive to 0.2 μg/ml. After administering a single 300-mg oral dose to human subjects, the average paramethadione serum levels of 6.0 μg/ml occurred at 1 hr and decreased to 0.3 μg/ml after 48 hr. Metabolite serum levels gradually increased to 8.4 μg/ml at 32 hr and were still at this level at 48 hr, which was the last sampling point.