Active secretion of the fluoroquinolone ciprofloxacin by human intestinal epithelial Caco‐2 cell layers

Abstract
The bidirectional transepithelial fluxes of ciprofloxacin, an antibacterial fluoroquinolone, across the human intestinal epithelial Caco‐2 cell‐line show marked asymmetry. Basal‐to‐apical flux of ciprofloxacin (10 μm) exceeds apical‐to‐basal flux indicating net secretion. Net ciprofloxacin secretion is abolished by azide/2‐deoxy‐d‐glucose treatment, displays saturation kinetics (Km = 0.89 ± 0.23 mm, Vmax 44.3 ± 4.9 nmol cm−2.h) and competition by other fluoroquinolones. A specific, active secretion in Caco‐2 epithelia may explain the transintestinal elimination of ciprofloxacin observed in pharmacokinetic studies in man.