Metabolic fate of phenobarbital in man. N-Glucoside formation.

1-(beta-D-Glucopyranosyl)phenobarbital was identified as the major metabolite of phenobarbital in man. Proof of structure was based on the comparison of the UV, NMR, and mass spectrometry and TLC data for the acetylated metabolite with an authentic compound. The previous erroneous structure assignment of this metabolite as N-hydroxyphenobarbital was based on insufficient data. After oral administration of 14C-labeled phenobarbital to two healthy male subjects, most of the radioactivity (87 and 78% of the dose) was recovered in urine over a period of 16 days. The N-glucopyranoside, p-hydroxyphenobarbital, and unchanged phenobarbital accounted for 30 and 24%, 18 and 19%, and 33 and 25% of the dose, respectively.