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Elmer Y. Tu, Megan E. Shoff, Charlotte E. Joslin; The Addition Of Benzalkonium Chloride To Moxifloxacin Confers Anti-acanthamoebal Activity In An In Vitro Model. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5830.
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Purpose: To determine the activity of moxifloxacin alone and moxifloxacin supplemented with lower concentrations of benzalkonium chloride (BAK) against acanthamoeba in an established in vitro model.
Methods: Trophozoites cultures of Acanthamoeba castellanii were incubated in non-nutrient amoeba saline + Enterobacter aerogenes. Three replicates of four solutions, moxifloxacin 0.5% alone, moxifloxacin 0.5% supplemented with BAK to achieve final concentrations of 0.001% and 0.003% and the unsupplemented amoeba saline acting as a control. Samples were taken at 30 minutes, and 1.5, 2.5, 4, 5.5, and 7 hours after exposureand immediately quanified. Amoeba counts were estimated using the most probable number method (MPN), as previously described, utilizing serial dilutions.
Results: MPN estimates showed no signficant reduction in the number of acanthamoeba organisms at any time point for moxifloxacin alone when compared to the control. Moxifloxacin + 0.001% BAK showed variable, modest reductions at all time points. Moxifloxacin + 0.003% BAK resulted in profound reductions ranging from 1.8 up to 3.9 log units versus control at all time points.
Conclusions: Moxifloxacin alone did not demonstrate any significant effect on acanthamoeba trophozoites in this established in vitro model. The addition of small concentrations of BAK, below that seen in many commercial eyedrop formulations can result in a significant and profound reduction in the number of acanthamoebal organisms with exposures of as little as 30 minutes. The contribution and exclusion of preservatives like BAK will need to be accounted for in the assessment, research and development of present and future ophthalmic medications and contact lens disinfection systems.
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