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  • Title: Characterization of the oral absorption of some beta-lactams: effect of the alpha-amino side chain group.
    Author: Oh DM, Sinko PJ, Amidon GL.
    Journal: J Pharm Sci; 1993 Sep; 82(9):897-900. PubMed ID: 8229687.
    Abstract:
    The intestinal absorption mechanisms of cefixime, 7-aminocephalosporanic acid (7-ACA) and 6-aminopenicillanic acid (6-APA) were determined from the results of single-pass perfusion experiments in rats by modified boundary layer analysis. The estimated absorption parameters (SEM) were as follows: for cefixime, J*max = 0.016 (0.008) mM, Km = 0.031 (0.015) mM, P*m = 0.184 (0.037), P*c = 0.523 (0.051); for 7-ACA, J*max = 6.39 (1.57) mM, Km = 19.33 (5.64) mM, P*c = 0.33 (0.03) mM; and for 6-APA, P*m = 0.41 (0.11), where J*max is the maximal flux of peptide transport system, Km is the intrinsic Michaelis constant, P*m is the dimensionless membrane permeability, and P*c is the dimensionless carrier permeability. Cefixime was absorbed by a carrier-mediated mechanism because its wall permeability (P*w) was concentration dependent and significantly inhibited by cephradine. A concentration-dependent permeability of 7-ACA was observed, but an inhibition study failed to show significant inhibition by cephradine. The absorptions of 6-APA and penicillin V were not inhibited by cephradine or cefixime. The fractions of dose absorbed of several beta-lactam antibiotics correlated well with their absorption numbers obtained from P*w values in rats. These results further demonstrate that an alpha-amino group is not necessary for transport by the intestinal peptide transporter.
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