CIPROFLOXACIN VERSUS TOBRAMYCIN FOR THE TREATMENT OF STAPHYLOCOCCAL KERATITIS

Purpose. To compare the chemotherapeutic efficacies of ciprofloxacin ( 0.3%) and fortified (1.36%) tobramycin for the treatment of methicilli n-sensitive and methicillin-resistant Staphylococcus aureus keratitis during early and late stages of infection. Methods. Rabbit corneas wer e intrastromally injected with 10(2) colony-forming units (CFU) of met hicillin-sensitive S. aureus (MSSA) or methicillin-resistant S. aureus (MRSA). Topical therapy was initiated at either 4 hours postinfection (early stage) or at 10 hours postinfection (late stage). Drops were a dministered every 15 minutes for 5 hours. Corneal bacterial counts and aqueous humor antibiotic concentrations were determined. Results. Ear ly administration of ciprofloxacin sterilized all MSSA-infected cornea s and 83% of MRSA-infected corneas. Late administration of ciprofloxac in reduced the numbers of viable MSSA and MRSA to 3.6 and 3.7 log(10) CFU per cornea, respectively, but did not sterilize any corneas. Early administration of fortified (1.36%) tobramycin sterilized all MSSA-in fected corneas but none of the MRSA-infected corneas. Late administrat ion of tobramycin reduced the viable MSSA to very low numbers (0.5 and 0.0 log(10), respectively) and sterilized 33% of MSSA-infected cornea s, but had little effect on MRSA-infected corneas. Conclusions. Early in infection, ciprofloxacin was highly effective against MSSA and MRSA , whereas tobramycin was effective only against MSSA. During later sta ges of infection, tobramycin was more effective than ciprofloxacin aga inst MSSA, and neither antibiotic was effective against MRSA. Thus, ci profloxacin is limited by the time of application and tobramycin is li mited by the resistance of the MRSA strain.