Ciprofloxacin versus tobramycin for the treatment of staphylococcal keratitis.
OBJECTIVE
To compare the chemotherapeutic efficacies of ciprofloxacin (0.3%) and fortified (1.36%) tobramycin for the treatment of methicillin-sensitive and methicillin-resistant Staphylococcus aureus keratitis during early and late stages of infection.


METHODS
Rabbit corneas were intrastromally injected with 10(2) colony-forming units (CFU) of methicillin-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 administered every 15 minutes for 5 hours. Corneal bacterial counts and aqueous humor antibiotic concentrations were determined.


RESULTS
Early administration of ciprofloxacin sterilized all MSSA-infected corneas and 83% of MRSA-infected corneas. Late administration of ciprofloxacin reduced the numbers of viable MSSA and MRSA to 3.6 and 3.7 log10 CFU per cornea, respectively, but did not sterilize any corneas. Early administration of fortified (1.36%) tobramycin sterilized all MSSA-infected corneas but none of the MRSA-infected corneas. Late administration of tobramycin reduced the viable MSSA to very low numbers (0.5 and 0.0 log10, respectively) and sterilized 33% of MSSA-infected corneas, 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 stages of infection, tobramycin was more effective than ciprofloxacin against MSSA, and neither antibiotic was effective against MRSA. Thus, ciprofloxacin is limited by the time of application and tobramycin is limited by the resistance of the MRSA strain.
Callegan
M C
MC
Department of Microbiology, Louisiana State University Medical Center School of Medicine, New Orleans.
Engel
L S
LS
Hill
J M
JM
O'Callaghan
R J
RJ
D000818:Animals; D002939:Ciprofloxacin / Q000008:administration & dosage* / Q000627:therapeutic use; D015169:Colony Count, Microbial; D003319:Corneal Stroma / Q000187:drug effects / Q000382:microbiology; D004334:Drug Administration Schedule; D015818:Eye Infections, Bacterial / Q000188:drug therapy*; D007634:Keratitis / Q000188:drug therapy* / Q000382:microbiology; D016106:Methicillin Resistance; D009883:Ophthalmic Solutions; D011817:Rabbits; D013203:Staphylococcal Infections / Q000188:drug therapy*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000254:growth & development; D014031:Tobramycin / Q000008:administration & dosage* / Q000627:therapeutic use
D009883:Ophthalmic Solutions; D002939:Ciprofloxacin; D014031:Tobramycin