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(R) (0.3% tobramycin), tobramycin (0.3%) in the Tobrex(R) vehicle with 0.05% dodecyl maltoside (DDM)/4.0% hydroxypropylmethycellulose (HPMC), Ocuflox(R) (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(R) Tobrex(R), or DDM/HPMC vehicle did not significantly reduce the log CFU (P greater than or equal to0.4837). Rabbits treated at 1 hour prior to infection with Ocuflox(R) 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 less than or equal to0.0001). Neither Tobrex(R) nor the DDM/HPMC vehicle significantly reduced the CFU/cornea compared to the untreated group (P greater than or equal to0.2312). 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.