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A. Blanco, M. Mezzatesta, F. Gona, A. Sudano Roccaro, M. G. Mazzone, S. Stefani; Antibacterial Activity of Netilmicin and Netilmicin/Dexamethasone Fixed Combination Against the Most Common Ocular Isolates. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2664.
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This study compared the activity of netilmicin with tobramycin and chloramphenicol against the most important pathogens isolated from ocular infections; killing curves with netilmicin and netilmicin/dexamethasone fixed combination (Netildex) were also performed to investigate if dexamethasone phosphate could improve netilmicin bactericidal activity.
Microdilution method, performed according to the Clinical and Laboratory Standards Institute guidelines (2008), was used to determine the Minimum Inhibitory Concentrations values (MICs) of netilmicin, tobramycin and chloramphenicol against the following 160 strains: S.pyogenes (15) S.pneumoniae (13), S.aureus (24), S.epidermidis (16),other CoNS (13), H.influenzae (15), M.catarrhalis (10), Proteus spp (32), P.aeruginosa (14) and Enterobacteriaceae (8). Killing curves at 1x, 2x, and 4xMICs of netilmicin or Netildex were also carried out against 14 strains.
Netilmicin showed MIC90 values ranging between 0.25 and 8 µg/ml, and all the isolates tested were netilmicin sensitive. Conversely, tobramycin and chloramphenicol resulted less active with higher MIC90 values (between 0.25 and 128 µg/ml, and between 1 and 256 µg/ml, respectively). In addition, 11.25% of the strains were resistant to tobramycin and 60.8% to chloramphenicol. Moreover, the killing kinetic studies showed how, in presence of dexamethasone, netilmicin had a faster kinetic, exerting its activity in the first eight hours against all of the 14 strains tested. In the same period, the antibiotic alone resulted bactericidal only for 9 of the 14 strains, showing however its full antibacterial efficacy at 24 hours, as espected.
Netilmicin - a third generation aminoglycoside antibiotic - showed the best antibacterial activity in vitro against ocular pathogens. Moreover, netilmicin and dexamethasone -a strong fluorinated synthetic corticosteroid- proved to be a successful combination to treat and resolve ocular infections, as also shown in vivo by several papers that support the efficacy of steroids administered in combination with antibiotics.
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