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Department of Anesthesiology and Intensive Care Medicine (T.N.,
Y.O., M.F.) and
Laboratory of Chemistry (S.I., Y.F.), Osaka City
University Medical School
To elucidate the effect of cytochrome P450 levels in hepatic
microsomes on the metabolism of lidocaine in vivo, we
investigated the metabolism of lidocaine in untreated (UT group) and
phenobarbital-treated rats (PB group) in vivo and compared
the results with those obtained by immunoblotting of rat hepatic
microsomes. There were no differences in pharmacokinetic parameters for
lidocaine between the UT and PB groups. The plasma concentrations
of the N-deethylated metabolite of lidocaine,
monoethyl-glycinexylidide (MEGX), in the PB group were significantly
higher than those in the UT group. On the other hand, the plasma
concentrations of the aromatic ring hydroxylated metabolite of
lidocaine, 3-hydroxylidocaine (3-OH LID), were significantly lower in
the PB group than in the UT group. When lidocaine metabolism was
studied with hepatic microsomes prepared from rats in the UT and PB
groups, the rates of formation of MEGX were higher in the microsomes of
the PB group than in those of the UT group. The contents of CYP2B1 and
3A2 in rat hepatic microsomes of the PB group measured by
immunoblotting were significantly higher than those of the UT group.
Strong correlations were found between the area under the plasma
concentration vs. time curve for MEGX and specific contents
of CYP2B1 and 3A2. These findings suggest that formation of MEGX
in vivo is dependent on the levels of CYP2B1 or 3A2 in rat
liver.
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