EFFECTIVENESS OF SPECIFIC ANTIBIOTIC STEROID COMBINATIONS FOR THERAPYOF EXPERIMENTAL PSEUDOMONAS-AERUGINOSA KERATITIS

Ciprofloxacin and prednisolone, but not an aminoglycoside and dexameth asone, were previously found to be effective in killing bacteria and r educing inflammation for the treatment of Pseudomonas keratitis. We in vestigated the therapeutic effectiveness of tobramycin/prednisolone an d ciprofloxacin/dexamethasone in a rabbit model of experimental kerati tis to increase our understanding of the effectiveness of antibiotic/s teroid combinations. To our knowledge, this is the first analysis of t he effectiveness of a combination of ciprofloxacin and dexamethasone f or experimental keratitis. Two experiments were conducted. In the firs t experiment, 36 rabbits were divided into six groups: 1) untreated; 2 ) prednisolone aeetate, 1.0%; 3) prednisolone phosphate, 1.0%; 4) tobr amycin, 1.36%; 5) tobramycin plus prednisolone acetate; 6) tobramycin plus prednisolone phosphate. In the second experiment, 23 rabbits were divided into four groups: 1) untreated; 2) ciprofloxacin, 0.3%, plus dexamethasone alcohol, 0.1%; 3) ciprofloxacin; 4) dexamethasone alcoho l. Topical antibiotic and/or steroid was given for 10 h, from 16 to 26 h postinfection, one drop every 15 min for the first hour and then ev ery 30 min for the remaining 9 h. At 27 h postinfection, eyes were eva luated by slit lamp examination (SLE) and assayed for the presence of bacteria in terms of colony forming units (CFU) per cornea. Both predn isolone acetate and prednisolone phosphate reduced ocular inflammation (as determined by SLE), compared with no treatment (P less than or eq ual to 0.036); the phosphate was more effective (P = 0.005). Tobramyci n alone and in combination with prednisolone also significantly reduce d SLE, compared with no treatment (P less than or equal to 0.006). The bactericidal activity of tobramycin was not affected by either steroi d formulation. In contrast, neither dexamethasone nor ciprofloxacin al one or in combination affected inflammation, although ciprofloxacin wa s equally effective in reducing bacterial CFU with or without the ster oid. These studies of experimental Pseudomonas keratitis suggest that prednisolone is superior to dexamethasone in reducing ocular inflammat ion and is compatible with the bactericidal activity of either tobramy cin or ciprofloxacin.