Mechanisms of Intestinal Absorption of the Antibiotic, Fosfomycin, in Brush-Border Membrane Vesicles in Rabbits and Humans

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In order to clarify the mechanism of intestinal absorption of an antibiotic, fosfomycin (FOM), the uptakes of FOM by rabbit and human small intestinal brush-border membrane vesicles (BBMV) were studied. The initial uptake of FOM by BBMV at 15 s was saturable at a higher concentration of FOM. The kinetic parameters at 37℃ of the saturable uptake expressed by the Michaelis-Menten equation were K_1=5.17 mM and J_<max>=3.88 nmol/15 s/mg protein for rabbits, and K_1=4.03 mM and J_<max>=1.90 nmol/15 s/mg protein for humans. The most efficient uptake was observed in the presence of both inward-directed Na^+-and H^+-gradients in both mammals. The uptake of FOM was inhibited by inorganic phosphate, FOM glycol which is a degradation product of FOM in the gastric juice and specific inhibitors of phosphate transport such as arsenate and phosphonoacetic acid. These findings confirmed that FOM absorption from rabbit and human small intestines is associated with the phosphate transport system. These transport phenomena of FOM are in close agreement with those obtained previously in rat BBMV studies. Judging from the results obtained for three mammalian species, rat, rabbit and human, it was concluded that carrier-mediated transport via the phosphate transport system is a very important pathway of intestinal absorption of FOM.
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