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C. C. McCormick, C. L. Balzli, A. R. Caballero, A. Tang, R. J. O'Callaghan; The Bactericidal Effectiveness of an EnhancedTobramycin-Dexamethasone Formulation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):846. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the bactericidal effectiveness of Tobradex ophthalmic suspension to a new formulation containing half the concentration of dexamethasone enhanced with novel suspension technology using rabbit models of Staphylococcus aureus and Pseudomonas aeruginosa keratitis.
Eyes were intrastromally injected with 100 colony forming units (CFU) of methicillin-sensitive S. aureus (MSSA; 8325-4) or methicillin-resistant S. aureus (MRSA; strain 70490) or 1000 CFU P. aeruginosa (27853). S. aureus infected eyes were treated every hour from 10 to 15 hours postinfection (PI) with a single drop of formulation. Eyes infected with Pseudomonas were treated at 16 hours PI with a single drop every 15 minutes for one hour and then every hour from 17 to 22 hours PI. Tested were untreated eyes (n = 12 per strain) and eyes treated with dexamethasone (0.1%, Maxidex; n = 6 per strain), tobramycin (0.3%, Tobrex; n = 6 per strain), the standard combination of tobramycin (0.3%) and dexamethasone (0.1%) (Tobradex, n = 6 per strain) or a new formulation of tobramycin (0.3%) and dexamethasone (0.05%) with pharmaceutical-grade xanthan gum (Tobradex ST; n = 6 per strain). Corneas were cultured 1 hour after the last treatment to determine the log CFU ± SEM per cornea.
Corneas in untreated eyes infected with MSSA or MRSA at 16 hours PI had 6.73 ± 0.1 and 6.95 ± 0.08 logs of bacteria, respectively; for P. aeruginosa, 7.55 ± 0.09 logs of bacteria were present at 23 hours PI. All eyes treated with Maxidex had no significant reduction in CFU as compared to the untreated control (P ≥ 0.15). Eyes treated with Tobrex had a significant reduction in CFU in MSSA-infected or MRSA-infected corneas (P = 0.002 and 0.04, respectively). Tobrex did not significantly reduce the CFU of P. aeruginosa (P = 0.09). Tobradex formulation significantly reduced the CFU in either Staphylococcus model (P ≤ 0.008), but not in the Pseudomonas model (P = 0.07). The Tobradex ST formulation in both Staphylococcus models significantly reduced the CFU per cornea relative to untreated eyes (P ≤ 0.003) and relative to eyes treated with the Tobradex formulation (P ≤ 0.01). The Tobradex ST in the Pseudomonas model also caused a significant reduction in CFU as compared to untreated controls (P = 0.007) and to eyes treated with the Tobradex formulation (P = 0.03).
The Tobradex ST formulation is effective for S. aureus and P. aeruginosa keratitis in a rabbit model.
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