Treatment of experimental Pseudomonas keratitis using collagen shields containing tobramycin

To study the effectiveness of collagen shields containing tobramycin sulfate in the treatment of Pseudomonas keratitis, rabbits were infected via an intrastromal injection of Pseudomonas aeruginosa and treated 22 hours later with either collagen corneal shields rehydrated in 4% tobramycin and applied to the cornea or 4% tobramycin drops. Bacterial killing was quantitated by culturing corneal homogenates and calculating the number of viable bacteria (colony-forming units) per cornea. Corneas receiving shields rehydrated in 4% tobramycin and applied for four hours demonstrated significantly reduced numbers of bacteria compared with untreated control corneas. The collagen shields were as effective in reducing the number of viable bacteria per cornea as 4% tobramycin drops applied every 30 minutes over a four-hour period. Over a nine-hour treatment period, the addition of four drops of 4% tobramycin to shields in situ was as effective as exchange with a new shield rehydrated in 4% tobramycin. These results suggest that collagen shields rehydrated in a water-soluble antibiotic such as tobramycin may be an effective and convenient mode of therapy for Pseudomonas keratitis.