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M.C. Callegan, B. Novosad; Efficacy of Fourth–Generation Fluoroquinolones Against Gram–Positive Species Commonly Involved in Ocular Infections . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1926.
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Staphylococcus epidermidis, Staphylococcus aureus (methicillin–sensitive and methicillin–resistant), Streptococcus pneumoniae, and Streptococcus viridans are frequently involved in ocular infections. We determined the minimal inhibitory concentrations (MICs) against these species for the ophthalmic formulations of fourth–generation fluoroquinolones, gatifloxacin 0.3% ophthalmic solution (Zymar), and moxifloxacin 0.5% ophthalmic solution (Vigamox), as well as MICs for solutions prepared from injectable powder forms of gatifloxacin and moxifloxacin. Because gatifloxacin 0.3% ophthalmic solution is preserved with 0.005% benzalkonium chloride (BAK), we also investigated the effect of BAK on MIC values.
At least 6 ocular isolates of each species were analyzed. MICs were determined by microdilution methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS) guidelines, in cation–adjusted Mueller Hinton broth for staphylococcal species, and the same medium supplemented with 2% lysed horse blood for streptococcal species. When present, BAK was 0.005%. 18–hour cultures of the test strains were diluted to approximately 105 CFU/mL for inoculation. Assays were incubated overnight at 37 C and growth determined spectrophotometrically (OD650) and by plating MIC test wells onto blood agar.
For gatifloxacin (powder), moxifloxacin (powder), and Vigamox, all without BAK, MICs for S. epidermidis ranged from 0.24–0.98 µg/mL, MICs for methicillin–sensitive S. aureus ranged from 0.06–0.24 µg/mL, MICs for methicillin–resistant S. aureus ranged from 1.95–15.6 µg/mL, MICs for S. pneumoniae ranged from 0.01–0.49 µg/mL, and MICs for S. viridans ranged from 0.12–0.49 µg/mL. MICs for Zymar (which contains BAK) and gatifloxacin powder supplemented with BAK were < 0.03 µg/mL for all strains tested. For all but 2 strains examined, the MIC for gatifloxacin 0.3% ophthalmic solution plus BAK was 2– to 260–fold less than for Vigamox. Addition of BAK to gatifloxacin powder resulted in a similar improvement in MIC values.
Gatifloxacin 0.3% ophthalmic solution with 0.005% BAK (Zymar) showed greater efficacy against Gram–positive species than moxifloxacin 0.5% ophthalmic solution (Vigamox). This superior potency was demonstrated for both Zymar and for gatifloxacin powder plus 0.005% BAK, suggesting that gatifloxacin and BAK work synergistically to lower MICs.
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