Comparison of intravitreal vancomycin and daptomycin application in experimental methicillin-resistant Staphylococcus aureus (MRSA) endophthalmitis in rabbits.

Purpose: To compare bactericidal activities of daptomycin and vancomycin in an experimental rabbit model of methicillin-resistant Staphylococcus aureus (MRSA) endophthalmitis.

Methods: The right eyes of 19 New Zealand rabbits weighing 2 to 2.5 kg were used. Each eye was inoculated with 1000 colony-forming units (cfu) of MRSA into the vitreous cavity. 24 h after the inoculation, the rabbits were randomly distributed into three groups: control group (n = 5) was given 0.1 ml of balanced saline solution, daptomycin group 2 (n = 7) was given 0.2 mg/0.1 ml daptomycin and vancomycin group 3 (n = 7) was given 1 mg/0.1 ml vancomycin intravitreally. Clinical examination scores were recorded and vitreous aspirates were obtained for microbiological analysis on days 2 and 3 after MRSA inoculation. Rabbits were sacrificed, and the eyes were enucleated for histopathological examination.

Results: There was no difference between the daptomycin group, vancomycin group and control in terms of the clinical grading of endophthalmitis 24 h after the inoculation. In all treatment groups, mean number of cfu and histopathological scores were significantly lower compared to the control group. There was no difference between the daptomycin and vancomycin group in terms of the histopathological and clinical examination scores. Culture negativity achieved on day 3 was 71.4% and 57.1% in the daptomycin treatment group and the vancomycin treatment group, respectively.

Conclusions: Although both daptomycin and vancomycin are effective in treatment of experimental MRSA endophthalmitis, daptomycin has superior bactericidal activity 72 h after inoculation.