Secretory mechanisms of grepafloxacin and levofloxacin in the human intestinal cell line Caco-2

Grepafloxacin and levofloxacin transport by Caco-2 cell monolayers was examined to characterize the intestinal behavior of these quinolones. The levels of transcellular transport of [¹⁴C]grepafloxacin and [¹⁴C]levofloxacin from the basolateral to the apical side were greater than those in the opposite direction. The unidirectional transport was inhibited by the presence of excess unlabeled quinolones, accompanied by increased accumulation. The inhibitory effects of cyclosporin A plus grepafloxacin on basolateral-to-apical transcellular transport and cellular accumulation of [¹⁴C]grepafloxacin were comparable to those of cyclosporin A alone, indicating that the transport of grepafloxacin across the apical membrane was mainly mediated by P-glycoprotein. On the other hand, basolateral-to-apical transcellular transport of [¹⁴C]levofloxacin in the presence of cyclosporin A was decreased by unlabeled levofloxacin, grepafloxacin, and enoxacin, accompanied by significantly increased cellular accumulation. The organic cation cimetidine, organic anion p-aminohippurate, and the multi-drug resistance-related protein (MRP) modulator probenecid did not affect the transcellular transport of [¹⁴C]grepafloxacin or [¹⁴C]levofloxacin in the presence of cyclosporin A. The basolateral-to-apical transcellular transport of levofloxacin in the presence of cyclosporin A showed concentration-dependent saturation with an apparent Michaelis constant of 5.6 mM. In conclusion, these results suggested that basolateral-to-apical flux of quinolones was mediated by P-glycoprotein and a specific transport system distinct from organic cation and anion transporters and MRP.