Antibiotic therapy of experimental Pseudomonas keratitis in guinea pigs
S. D. Davis, L. D. Sarff and R. A. Hyndiuk
Antibiotic therapy of experimental Pseudomonas keratitis was evaluated
quantitatively by determining numbers of viable bacteria in the cornea of
guinea pigs. Topically applied carbenicillin disodium, gentamicin sulfate,
and tobramycin sulfate were often significantly more effective than
topically applied polymyxin B sulfate. Intramuscular therapy with
tobramycin was as effective as topical therapy, and the results exhibited
less variability. Topical tobramycin every 30 minutes was significantly
more effective than topical therapy every 60 minutes. No combination of
antibiotics was significantly better than a single effective drug. The
concentration of tobramycin in the aqueous correlated more closely to
therapeutic efficacy than did the concentration in the cornea. Although all
antibiotics reduced numbers of bacteria in the cornea by more than 99% in
the first 24 hours of therapy, none was able to sterilize the cornea in
four additional days of continuous therapy. Persistence of organisms
despite apparently adequate topical therapy may explain some reported cases
of relapse in humans.
