The intestinal transport mechanism of fluoroquinolones: inhibitory effect of ciprofloxacin, an enoxacin derivative, on the membrane potential-dependent uptake of enoxacin.

PURPOSE: To clarify the absorption-structure relationship for the fluoroquinolones from the point of view of inhibitory behavior.
METHODS: The inhibitory effects of ciprofloxacin on the transport process of enoxacin across the rat intestinal brush-border membrane was examined.
RESULTS: Ciprofloxacin, which has a similar structure to enoxacin, exhibited a pH-dependent interference with enoxacin absorption from rat jejunal loops. The uptake experiments using BBM vesicles showed that ciprofloxacin significantly reduced not only the initial binding of enoxacin to the membrane surface, but also the K(+)- or H(+)-diffusion potential-dependent transport across the membrane. Furthermore, an H(+)-diffusion potential (interior negative) also exhibited a stimulative uptake of ciprofloxacin.
CONCLUSIONS: These results suggest that the inhibition behavior of ciprofloxacin from the jejunal loop was closely related to the ionic diffusion potential-dependent uptake of enoxacin across the brush-border membrane.