| Summary: | ABSTRACT Purpose: To compare the aqueous humor (AH) concentrations of moxifloxacin 0.5% and gatifloxacin 0.3% solutions alone or when treatment was combined with steroids, and to correlate these concentrations with the minimum inhibitory concentrations (MIC) for the most common endophthalmitis-causing organisms. Methods: Patients undergoing phacoemulsification were enrolled to receive one drop of one of the following solutions: moxifloxacin (G1), moxifloxacin + dexamethasone (G2), gatifloxacin (G3), or gatifloxacin + c (G4), every 15 min, 1h before surgery. AH samples were collected before surgery and analyzed using HPLC-tandem mass spectrometry. Results: The mean antibiotic concentrations in the AH were: G1= 1280.8 ng/mL; G2= 1644.3 ng/mL; G3= 433.7 ng/mL; and G4= 308.1 ng/mL. The mean concentrations statistically differed between G1 and G2 (p=0.01), and G3 and G4 (p=0.008). All samples achieved the MIC for Staphylococcus epidermidis; 100% of the samples from G1 and G2, and 97% from G3 and G4 reached the MIC for fluoroquinolone-sensitive Staphylococcus aureus; 100% of the samples from G1 and G2, 88% from G3, and 72% from G4 reached the MIC for enterococci (p<0.001); and 100% of samples from G1 and G2, 59% from G3, and 36% from G4 reached the MIC for Streptococcus pneumoniae (p<0.001). For fluoroquinolone-resistant S. aureus, 23% from G1, 44% from G2, and no samples from G3 or G4 achieved the MIC (p<0.001). Conclusions: Moxifloxacin + dexamethasone demonstrated a higher concentration in the AH than the moxifloxacin alone. Gatifloxacin + steroids demonstrated less penetration into the anterior chamber than gatifloxacin alone. Moxifloxacin was superior to gatifloxacin considering the MIC for enterococci, S. pneumoniae, and fluoroquinolone-resistant S. aureus.
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