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Takashi Suzuki, Toshihiro Yamamoto, Yuichi Ohashi; Bactericidal Activity of Levofloxacin against Staphylococcus aureus and Staphylococcus epidermidis in an In Vitro Pharmacokinetic Model Simulating Concentration in the Bulbar Conjunctiva after Eye Drop. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5785.
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The aim of this work was to compare the pharmacological properties of levofloxacin (LVFX) against Staphylococcus aureus and Staphylococcus epidermidis by pharmacokinetic (PK) model simulating concentration in the bulbar conjunctiva after eye drop of 0.5% and 1.5% LVFX.
The strains used were S. aureus and S. epidermidis conjunctival sac isolates which minimum inhibitory concentrations (MICs) of LVFX were 0.25 and 0.125 μg/ml, respectively. The LVFX resistant strains were made from their parental strains by culture with LVFX. The in vitro PK model simulated the concentration of the bulbar conjunctiva following topical application of 0.5 or 1.5% LVFX ophthalmic solution three times (0, 4 and 8 hour) to rabbit eyes. Parental and LVFX resistant strains were exposed to LVFX in an in vitro PK model, and changes in viable bacterial counts were evaluated over the course of 12h.
MICs of LVFX in resistant isolates increased from 2 to 32 times of parental strains (S. aureus; 0.5-2μg/ml, S. epidermidis; 0.5-4μg/ml) after induction of LVFX resistance. LVFX was bactericidal against all tested strains which MICs included highest value, in PK model simulating use of 1.5% LVFX ophthalmic solution. In contrast, simulation of 0.5% LVFX eye drop showed LVFX was bactericidal against isolates which MICs were as follows: (S. aureus; 0.25-0.5μg/ml, S. epidermidis; 0.125-1μg/ml).
In vitro PK model simulating concentration in the bulbar conjunctiva after LVFX eye drop demonstrated 1.5% LVFX ophthalmic solution had stronger bactericidal effects against Staphylococci in the bulbar conjunctiva than 0.5% LVFX ophthalmic solution.
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