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J.M. Blondeau, S. Borsos; Antimicrobial Efficacy of Gatifloxacin With and Without Benzalkonium Chloride Compared With Moxifloxacin Against Methicillin–Resistant Staphylococcus Aureus . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1903.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the antimicrobial efficacy of gatifloxacin with and without benzalkonium chloride (BAK) and unpreserved moxifloxacin against methicillin–resistant Staphylococcus aureus (MRSA).
Sixty–seven clinical isolates of MRSA were evaluated. Minimum inhibitory concentration (MIC) testing was by microbroth dilution in accordance with the recommended CLSI procedure. Approximately 105 CFU/ml of methicillin resistant S. aureus was added to Mueller–Hinton broth containing two–fold concentration increments of drug. For the evaluation of gatifloxacin with BAK, 2.5 µl of a 10% solution was added to the first well of the plate to give a BAK concentration of 0.125%, and then was serially diluted with the drug; subsequently diluted at 1:2 when adding organisms to each well. Plates were incubated for 18 hours in ambient air and the lowest concentration showing no growth was recorded as the MIC. In separate experiments, the growth of 30 MRSA isolates was tested in appropriate media containing two–fold concentration increments of Zymar (each well was adjusted to contain 0.005% BAK –– the percentage in the formulated product).
The combination of gatifloxacin with BAK was more efficacious than either fluoroquinolone without BAK. MIC values ranged from 0.008 µg/ml to 0.125 µg/ml for gatifloxacin plus BAK, from 0.063 µg/ml to 8 µg/ml with unpreserved gatifloxacin, and from 0.016 µg/ml to 16.0 µg/ml with moxifloxacin. In the presence of 0.005% BAK and concentrations of Zymar (gatifloxacin oph solution which is preserved with 0.005% BAK) ranging from 0.016 µg/mL to 2 µg/mL, 30 independent MRSA isolates failed to grow; viable MRSA were recovered from only 5/48 wells.
In this study of MRSA clinical isolates in vitro, the combination of gatifloxacin and BAK provided MIC values that were approximately 2– to 500–fold better than the MIC values provided by gatifloxacin or moxifloxacin alone. These findings may have important clinical relevance because commercial gatifloxacin ophthalmic solution (Zymar) is preserved with 0.005% BAK and commercial moxifloxacin is unpreserved.
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