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Joseph M. Blondeau, Shantelle D. Borsos, Leah D. Blondeau, Brandon J. Blondeau; Rapid Killing Of Contemporary Ocular Staphylococcus Epidermidis (se) And Methicillin Resistant Staphylococcus Aureus (mrsa) Isolates By Clinically Relevant Zymaxid Drug Concentrations. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1501.
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To determine the killing of contemporary ocular SE and MRSA isolates by Zymaxid (gatifloxacin 0.5% plus benzalkonium chloride [BAK] 0.0005%) at clinically relevant drug concentrations.
For kill experiments, contemporary clinical ocular SE (n=4) and MRSA (n=4) isolates were grown in Mueller-Hinton broth and 105 colony forming units/milliliter were exposed to Zymaxid (including BAK) at clinically relevant drug concentrations. The log10 reduction and percent kill of viable cells were recovered at 5, 10, 15, 20, 25, 30, 60, 120 and 180 minutes of drug exposure following incubation under ambient conditions. All kill measurements were done in triplicate and the results averaged.
Exposure of SE and MRSA strains to Zymaxid (including BAK) yielded a 0.37-1.24 log10 reduction (52-90% kill) by 5 min, 0.79-2.44 by 10 min (91-99% kill), 1.4-3.7 by 15 min (95-99.7% kill), 1.7-4.7 by 20 min (98-99.9% kill), 2.8-5.2 by 25 min (99-100% kill). Killing by BAK alone was less than for Zymaxid with BAK. For BAK alone, a 0.2-1.85 log10 reduction (40-96% kill) in viable cells was seen by 5-20 min following drug exposure. For BAK alone at 15ug/ml, 99-100% of cells were killed after 60 minutes of drug exposure. Resistance to methicillin did not affect killing by Zymaxid (including BAK).
Zymaxid contains 0.5% gatifloxacin (500ug/ml of gatifloxacin) and 0.0005% BAK (50ug/ml). Killing of SE and MRSA ocular strains by Zymaxid (including BAK) at clinically relevant drug concentrations resulted in a rapid reduction in viable cells (52-90% killing by 5 min and 99-100% by 25 min) and was greater than for BAK alone at 15ug/ml. Zymaxid is approved for dosing 2-4 times/day and our kill experiment results show rapid killing of contemporary ocular SE and MRSA strains at clinically relevant drug concentrations.
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