RT Journal Article
SR Electronic
T1 Qualitative and quantitative studies of methylphenobarbital metabolism in man.
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 381
OP 385
VO 9
IS 4
A1 W D Hooper
A1 H E Kunze
A1 M J Eadie
YR 1981
UL http://dmd.aspetjournals.org/content/9/4/381.abstract
AB The accumulation of methylphenobarbital (MPB) and phenobarbital (PB) in plasma in two volunteers who were given continuous once-daily oral doses of MPB for 3 weeks was demonstrated by use of a selected ion-monitoring GC/MS assay. It was shown that the PB concentration exceeded the MPB concentration in plasma after about day 4, and that both barbiturates achieved plateau concentrations after about 2 weeks. GC/MS studies on the urine of these volunteers permitted the identification of several new metabolites of MPB. These included 5-ethyl-5-(4-hydroxyphenyl)-1-methylbarbituric acid (p-OH-MPB), and the 3-O-methylcatechols of both MPB and PB. The meta-isomers of hydroxy-MPB and hydroxy-PB were identified in urine extracts, but were shown to be methodological artifacts. Quantitative studies, with use of a HPLC assay, were carried out for p-OH-MPB, PB and p-OH-PB in urine, and it was shown that these three substances collectively accounted for some 50% of the administered dose (greater than 30% as p-OH-MPB).