Fluoroquinolone−Biomembrane Interactions:  Monolayer and Calorimetric Studies

The interaction of two 6-fluoroquinolones, ciprofloxacin and its pentyl derivative, with model membranes was studied as a function of drug hydrophobicity as reflected in the pentyl side chain at position 4 in the piperazinyl group, by epifluorescence surface balance technique and differencial scanning calorimetry. In the first part of this study drug incorporation in dipalmitoylphosphatidylcholine monolayers was investigated using epifluorescence microscopy. In the second part, the influence of the presence of the hydrophobic chain and fluoroquinolone content on the thermotropic behavior of liposomes was investigated. Both monolayer and calorimetric studies demonstrated that hydrophobicity of the drug had a role in determining the nature of drug−membrane interaction as seen in greater perturbations of the lipid packing by pentyl ciprofloxacin.