Felbamate metabolism in the rat, rabbit, and dog

Two major and one minor metabolite of felbamate (FBM) as well as unchanged drug were isolated and identified by electron impact and chemical ionization mass spectrometry from rat and dog urine after dosing with [14C]FBM. The metabolites were 2-(4-hydroxyphenyl)-1,3-propanediol dicarbamate (p-OHF), 2-hydroxy-2-phenyl-1,3-propanediol dicarbamate, and 2-phenyl-1,3-propanediol monocarbamate. The metabolites and FBM were excreted mainly in urine, where their sum accounted to 81-94% of the radioactivity in hydrolyzed rat urine samples, 71-82% in rabbit urine samples, and 69-83% in dog urine samples. The amount of metabolites in the conjugated form was estimated to be 20-35% in rat, 20-30% in rabbit, and 10-20% in dog urine. The major biliary metabolite in all three species was p-OHF, whereas the amount of FBM was small. Metabolites found in dog feces were the same as those in the urine.