Cinoxacin: competitive inhibitory effect on p-aminohippurate transport and its uptake in renal cortical slices.

The effect of cinoxacin on p-aminohippurate (PAH) transport and the accumulation of cinoxacin were examined in renal cortical slices. Cinoxacin significantly inhibited the uptake of PAH by the slices from rats and rabbits. Cinoxacin increased the apparent Michaelis constant (Km) but did not affect Vmax for PAH uptake by rat kidney cortical slices, suggesting that cinoxacin inhibited PAH transport in a competitive manner. Cinoxacin was taken up but did not affect the cellular metabolism of Na+, K+ and ATP in the slices from rats and rabbits, except that 740 microM cinoxacin increased net Na+ efflux. These data indicate that cinoxacin is transported by the same process as that of PAH in renal cortical slices. Lastly, repeated administration of cinoxacin to rats did not affect the uptake of the drug by the slices.