The effectiveness of tobramycin and Ocuflox in a prophylaxis model of Staphylococcus keratitis.

PURPOSE

To determine the effectiveness of prophylactic antibiotic treatment prior to intra-corneal infection with Staphylococcus aureus.

METHODS

One topical drop of Tobrex (0.3% tobramycin), tobramycin (0.3%) in the Tobrex vehicle with 0.05% dodecyl maltoside (DDM)/4.0% hydroxypropylmethycellulose (HPMC), Ocuflox (0.3% ofloxacin) or DDM/HPMC vehicle were applied to rabbit eyes at one or five hours prior to injection of bacteria. Approximately 500 colony-forming units (CFU) of S. aureus strain 8325-4 were injected into the corneal stroma. Rabbits were sacrificed five hours after infection and corneal homogenates were cultured to determine the number of colony forming units (CFU) per cornea.

RESULTS

Rabbits treated at five hours prior to infection with tobramycin-DDM/HPMC reduced the bacterial load by approximately 2.4 log CFU/cornea as compared to the untreated control (3.47 +/- 0.98 vs. 5.71 +/- 0.14 log CFU/cornea, respectively; P = 0.0010); however, Ocuflox, Tobrex, or DDM/HPMC vehicle did not significantly reduce the log CFU (P >or= 0.4837). Rabbits treated at 1 hour prior to infection with Ocuflox or tobramycin-DDM/HPMC had significantly reduced CFU/cornea (1.31 +/- 0.86 and 0.48 +/- 0.31 log CFU/cornea, respectively) as compared to the untreated group (5.71 +/- 0.14 log CFU/cornea; P <or= 0.0001). Neither Tobrex nor the DDM/HPMC vehicle significantly reduced the CFU/cornea compared to the untreated group (P >or= 0.2312).

CONCLUSIONS

This pre-treatment model of Staphylococcus keratitis quantitatively measured the prophylactic effectiveness of topical antibiotic formulations. An important finding was that a tobramycin-DDM/HPMC formulation was highly effective as a prophylactic medication.