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  • 1
    Electronic Resource
    Electronic Resource
    Transport Characteristics of Ceftibuten (7432-S), a New Oral Cephem, in Rat Intestinal Brush-Border Membrane Vesicles: Proton-Coupled and Stereoselective Transport of Ceftibuten (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 302-307 
    Details
    ISSN: 1573-904X
    Keywords: ceftibuten ; proton-coupled uphill transport ; rat intestinal brush-border membrane vesicles ; stereoselective transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The transport characteristics of ceftibuten in rat intestinal brush-border membrane vesicles were investigated by a rapid filtration technique. Ceftibuten uptake was markedly stimulated by an inwardly directed H+ gradient (pH 7.5 inside, pH 5.5 outside) in comparison with that in the absence of a H+ gradient. The uptake at 30 sec was four times greater than that observed at equilibrium (overshoot phenomenon), while the H+ gradient-stimulated uptake of ceftibuten was markedly reduced in the presence of FCCP, a protonophore. These results suggested H+-coupled uphill transport of ceftibuten. In contrast, an inwardly directed Na+ gradient had no effect on ceftibuten uptake. The valinomycin-induced K+ diffusion potential (inside positive) significantly stimulated the ceftibuten uptake, suggesting net transfer of the negative charge. In contrast to the cis-isomer ceftibuten, the trans isomer of ceftibuten is not readily absorbed from the intestine, and its uptake was found not to be affected by a H+ gradient. Since the lipophilicity of the trans isomer is similar to that of ceftibuten, the uptake process appears to be stereoselective. The initial uptake of ceftibuten and its analogue cefaclor was concentration dependent under a H+ gradient. The apparent K m value was 0.2 mM for ceftibuten and 3.0 mM for cefaclor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015994323639
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  • 2
    Electronic Resource
    Electronic Resource
    Transport Characteristics of Ceftibuten, a New Oral Cephem, in Rat Intestinal Brush-Border Membrane Vesicles: Relationship to Oligopeptide and Amino β-Lactam Transport (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 308-312 
    Details
    ISSN: 1573-904X
    Keywords: ceftibuten ; transport ; brush-border membrane ; oligopeptide ; amino β-lactam ; oral cephem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ceftibuten undergoes H+-coupled uphill transport across rat small intestinal brush-border membrane vesicles. The effects of amino acids, peptides, folate, and β-lactams on the uptake of ceftibuten were examined. Uptake of ceftibuten was competitively inhibited by dipeptides or tripeptides. A counter-transport effect on ceftibuten uptake was observed in the vesicle preloaded with these peptides, and the transport was temporarily against a concentration gradient (overshooting). On the other hand, ceftibuten uptake was not changed by amino acids and a tetrapeptide. Therefore, ceftibuten is predominantly transported via the oligopeptide transport system in the brush-border membranes. The relationship of ceftibuten transport to folate and other oral antibiotics was also investigated. Cyclacillin, cephradine, and cefadroxil exhibited both inhibitory and countertransport effects, but folate, cefaclor, and cephalexin showed only a slight inhibitory effect. As the transport of cefaclor showed no uphill uptake in the presence of a H+ gradient and its H+ stimulated uptake was small, a H+ gradient-independent carrier-mediated system seems to participate in its transport. These findings suggest that two different carrier-mediated transport systems, H+ gradient dependent and independent, may exist for oral cephems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015946407709
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  • 3
    Electronic Resource
    Electronic Resource
    Stereoselective renal secretion of carbenicillin in rabbits: Role of the organic anion transporter at the renal brush border membrane (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 349-357 
    Details
    ISSN: 0899-0042
    Keywords: carbenicillin ; stereoselective ; secretion ; transport ; rabbit ; membrane vesicles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselectivity in the renal secretion of carbenicillin (CBPC) was studied in rabbits. Significant renal secretion of CBPC was observed in vivo, with the secretion of the S-epimer being greater than that of the R-epimer. Stereoselective transport of CBPC was further studied in vitro using basolateral and brush border membrane vesicles prepared from rabbit kidneys. The transport of CBPC by the organic anion transporter into the basolateral membrane vesicles (BLMV) was not stereoselective. In contrast, a distinct stereoselectivity was observed in the transport of CBPC by the organic anion transporter into the brush border membrane vesicles (BBMV), with the transport of the S-epimer being more favorable. Significant epimer-epimer interactions were also observed in the transport into BBMV. The stereoselectivity of the transport of CBPC was calculated from the kinetic parameters with consideration of epimer-epimer interactions and was similar to that observed in vivo. It was concluded that the observed stereoselectivity in the renal secretion of CBPC in vivo reflected that of transport via the organic anion transporter located at the brush border membrane. Chirality 10:349-357, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stereoselective pharmacokinetics of ibuprofen in rats: effect of enantiomer-enantiomer interaction in plasma protein binding (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 354-361 
    Details
    ISSN: 0899-0042
    Keywords: ibuprofen ; enantiomers ; stereoselective ; interactions ; plasma protein binding ; rat ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective pharmacokinetics of ibuprofen (IB) enantiomers were studied in rats. Unidirectional conversion from R-ibuprofen (R-IB) to S-ibuprofen (S-IB) was observed following intravenous administration. S-IB concentrations in plasma following racemate administration were simulated according to a conventional compartmental model using the parameters obtained after the administration of individual enantiomers, and resulted in overestimation of S-IB concentrations.Binding of IB enantiomers measured in rat plasma was stereoselective, the binding of R-IB being more favorable than that of S-IB. Moreover, there are interactions between IB enantiomers in binding, which may cause the increase of distribution volumes of IB enantiomers in the presence of their antipodes. Hence simulated S-IB concentrations according to a conventional compartment model were significantly greater than those observed. Indeed, when the enantiomer-enantiomer interactions were taken into account, simulation of S-IB concentrations in plasma following racemate administration was in good agreement with observed values. Therefore, interactions between stereoisomers as well as dispositional stereoselectivity have to be considered when pharmacokinetics of stereoisomers after administration of the racemate are compared to those after administration of individual isomers. Chirality 9:354-361, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Stereoselectivity and enantiomer-enantiomer interactions in the binding of ibuprofen to human serum albumin (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 643-649 
    Details
    ISSN: 0899-0042
    Keywords: ibuprofen ; stereoselective ; binding ; HSA ; interaction ; fluorescent ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of ibuprofen (IB) enantiomers to human serum albumin (HSA) was studied using a chiral fluorescent derivatizing reagent, which enabled the measurement of IB enantiomers at a concentration as low as 5 × 10-8 M. Scatchard analyses revealed that there were two classes of binding sites for both enantiomers. For the high affinity site, the number of the binding sites was one for both enantiomers, and the binding constant of R-IB was 2.3-fold greater than that of S-IB. The difference in the affinity at the high affinity site may result in the stereoselective binding of IB enantiomers at therapeutic concentrations. It was confirmed that the high affinity site of IB enantiomers is Site II (diazepam binding site) by using site marker ligands. Also, significant enantiomer-enantiomer interactions were observed in the binding. The binding data were quantitatively analyzed and a binding model with an assumption of competitive interactions only at the high affinity site simulated the binding characteristics of IB enantiomers fairly well. Chirality 9:643-649, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselective binding of carbenicillin epimers to human serum albumin (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 201-206 
    Details
    ISSN: 0899-0042
    Keywords: carbenicillin ; stereoselective ; binding ; HSA ; interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of carbenicillin (CBPC) epimers to human serum albumin (HSA) was found to be stereoselective. Epimer-epimer interaction was also observed in the binding to HSA. There were at least three binding sites on HSA for CBPC epimers, one of which (stereoselective site) was more in favor of S-CBPC than R-CBPC. At the stereoselective site, the binding constant of S-CBPC was approximately 4-fold greater than that of R-CBPC. The affinities to other binding sites (non-stereoselective sites) were similar between the epimers, and the affinity of S-CBPC of the non-stereoselective sites was much smaller than that for the stereoselective site.R-CBPC and S-CBPC appeared to displace each other at all the binding sites, i.e., the binding of the epimers was competitive at the non-stereoselective sites as well as at the stereoselective site. By using site marker ligands, it was revealed that CBPC epimers may bind to Site I (warfarin binding site), but not to Site II (diazepam binding site). A binding model with an assumption of competitive interactions at all the binding sites simulated the binding characteristics of CBPC epimers fairly well. © 1996 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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