Clearance of liposome-incorporated ciprofloxacin after intravitreal injection in rabbit eyes

Background Ciprofloxacin (CIP) is a fluoroquinolone-antibiotic with a high antimicrobial activity against all pathogens causing bacterial endophthalmi tis. After intravitreal injection, however, elimination half-life of this a ntibiotic is only 2.2 hours. To prolong intraocular bioavailability this st udy was performed to incorporate CIP into liposomes and to determine its cl earance from the vitreous after intravitreal injection. Materials and methods CIP was incorporated into multilamellar vesicles by m echanical dispersion. 0.1 mi of this suspension (equiv. 273.6 mu g CIP) was injected into the midvitreous of pigmented rabbit eyes (Chinchilla-bastard s). One day, 3 and 14 days after the injection intravitreal concentration o f CIP was determined by means of high-pressure-liquid-chromatography after dissolution of the liposomes by ultrasound. At the same intervals serum con centration of the antibiotic was examined as well. Results Within 24 hours intravitreal concentration fell to 18.0 mu g/ml. Th ree days after the injection the concentration of CTP was 6.9 mu g/ml. This is still above the minimal inhibitory concentration (MIC90) of the most co mmon ocular pathogens. At 14 days CIP was not detectable in the vitreous an y more. The serum concentration was between 0.04 mu g/ml and 0.07 mu g/ml. 3 and 14 days after injection no CIP could be detected. Conclusions This study shows that the incorporation of CIP into liposomes c an be achieved in sufficient doses by mechanical dispersion method. After i ntravitreal application the bioavailability of the antibiotic can be marked ly improved. Even after 3 days the intravitreal levels were above the MIC90 of the most common endophthalmitis pathogens.