Clarithromycin for experimental Staphylococcus aureus keratitis.
OBJECTIVE
Clarithromycin, a macrolide antibiotic not previously tested against the common causes of bacterial keratitis, was analyzed for its effectiveness in reducing the number of viable bacteria in a Staphylococcus keratitis model. An in vivo comparison of the effectiveness of clarithromycin to erythromycin, minocycline, and tetracycline for three strains of Staphylococcus aureus was done.


METHODS
Rabbit eyes were intrastromally injected with 100 colony forming units of one of three strains of S. aureus. Two strains were methicillin-sensitive (ATCC 25923 and MSSA 309) and one strain methicillin-resistant (COL). Eyes were treated every 30 minutes with 0.3% clarithromycin, erythromycin, tetracycline, or minocycline from 4 to 9 hours postinfection. The number of colony forming units (CFU) per cornea in all eyes was determined at 10 hours postinfection.


RESULTS
Vehicle-treated and untreated eyes (controls) contained over 6 logs of CFU per cornea, a value significantly higher than any of the antibiotic-treated eyes (P < or = 0.0001). Clarithromycin or erythromycin therapy significantly decreased the number of CFU per cornea by approximately 5 logs in the eyes infected with the methicillin-sensitive strains and by approximately 4 logs in the eyes infected with the methicillin-resistant strain. Tetracycline and minocycline were also successful in treating these strains, but overall showed less effectiveness than clarithromycin and erythromycin.


CONCLUSIONS
Clarithromycin proved to be an effective ocular medication for the therapy of experimental S. aureus keratitis. The effectiveness of clarithromycin in this model and its known effectiveness for a variety of bacterial pathogens suggests a role for this drug as a useful ocular antibiotic.
Hume
E B
EB
Department of Microbiology, Immunology, and Parasitology, LSU Medical Center, New Orleans, LA 70112, USA.
Moreau
J M
JM
Conerly
L L
LL
Cannon
B M
BM
Dajcs
J J
JJ
Hill
J M
JM
O'Callaghan
R J
RJ
D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D017291:Clarithromycin / Q000627:therapeutic use*; D015169:Colony Count, Microbial; D004917:Erythromycin / Q000627:therapeutic use; D007634:Keratitis / Q000382:microbiology*; D008911:Minocycline / Q000627:therapeutic use; D011817:Rabbits; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013752:Tetracycline / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D004917:Erythromycin; D013752:Tetracycline; D008911:Minocycline; D017291:Clarithromycin