Ofloxacin-loaded liposomes: In vitro activity and drug accumulation in bacteria

Different ofloxacin-loaded unilamellar vesicles were prepared by the extrus ion technique, and their antimicrobial activities were determined in compar ison to those of the free drug by means of MIC determinations with both Ame rican Type Culture Collection standards and wild-type bacterial strains (si x strains of Enterococcus faecalis, seven strains of Escherichia coli, six strains of Staphylococcus aureus, and six strains of Pseudomonas aeruginosa ). The accumulation of ofloxacin and liposome-ofloxacin was measured by det ermining the amount of the drug inside the bacteria as a function of time. Encapsulated fluoroquinolone yielded MICs which were at least twofold lower than those obtained with the free drug. In particular, liposomes made up o f dimyristoylphosphatidylcholine-cholesterol-dipalmitoylphosphatidylserine and dimyristoylphosphatidylcholine-cholesterol-dihexadecylphosphate (4:3:4 molar ratio) provided the best improvement in antimicrobial activity agains t the various bacterial strains investigated. The liposome formulation prod uced higher intracellular fluoroquinolone concentrations than those achieve d simultaneously with the free drug in both E. coli and P. aeruginosa.