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Shilpa Kodati, Andrew W Eller, Regis P Kowalski; Which Gram-Negative Antibiotic Complements Vancomycin for Broad-Spectrum Coverage of Endophthalmitis: Amikacin or Ceftazidime?. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4508. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Vancomycin (VAN) is established as first-line therapy in the treatment of Gram-positive (GP) bacterial endophthalmitis, while amikacin (AMK) or ceftazidime (CEF) are accepted for Gram-negative (GN) coverage. The in vitro susceptibility of GP and GN bacteria to VAN, AMK, and CEF were reviewed to evaluate the use of these antibiotics in the broad-spectrum treatment of bacterial endophthalmitis.
Bacteria isolated from endophthalmitis specimens collected from January 1st 1993 to December 31st 2013 were tested for in vitro susceptibility to VAN, AMK, and CEF using the Kirby Bauer disk diffusion method with serum breakpoint standard interpretations. Specimens were obtained from different combinations of anterior chamber, vitreous and vitrectomy samples.
1) 588 microbial isolates were identified. Coagulase negative Staphylococci (CoNS) were the most common bacteria (57.0%), followed by Streptococci (Strep) species (20.7%), Staphylococcus aureus (SA) (10.0%), GN bacteria (7.1%), and other Gram-positive (other-GP) bacteria (5.1%).2) All GP organisms were susceptible to VAN, with the exception of 1 Lactobacillus isolate. 12.2% of GN were susceptible to VAN.3) The in vitro susceptibility of bacteria to AMK were: CoNS (94.5%), SA (72.1%), Strep (7.4%), GN (90.2%), and other-GP (86.7%).4) The in vitro susceptibility of bacteria to CEF were: CoNS (57%), SA (50.8%), Strep (82.3%), GN (88.1%), and other-GP (48.3%).5) There was no difference between AMK (90.2%) and CEF (88.1%) for GN coverage.6) AMK (94.5%, 72.1%, and 86.7%) provided better coverage than CEF (57%, 50.8%, and 48.3%) for CoNS, SA, and other-GP bacteria respectively (p<0.005, FE).7) CEF (82.3%) appeared to provide better coverage (p<0.001, FE) for Strep than AMK (7.4%).
Based on in vitro studies, Vancomycin remains an optimal antibiotic choice for the treatment of Gram-positive endophthalmitis. AMK and CEF appear to provide equal GN coverage, but AMK provides better coverage for CoNS, SA, and other-GP, but not Strep. Despite the improved complementary coverage provided by AMK, retinal toxicity may be a concern.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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