Ocular concentration of gentamicin after penetrating keratoplasty

To determine if the storage of corneal tissue in a preserving medium containing gentamicin results in therapeutically effective concentrations of antibiotics in the ocular tissues after penetrating keratoplasty, we stored rabbit donor corneas in McCarey-Kaufman medium containing 100 micrograms of gentamicin per milliliter for three days before surgery. Gentamicin concentrations were determined by agar-diffusion bioassay in ocular tissues one, two, three, four, and six hours after surgery. On the average, the concentration of antibiotic one hour after surgery was 8.8 micrograms of gentamicin per gram of donor cornea, 6.25 micrograms of gentamicin per milliliter of iris, and 2.8 micrograms of gentamicin per milliliter of aqueous humor. The minimal inhibitory concentration for sensitive strains of Pseudomonas aeruginosa is 1.6 micrograms of gentamicin per milliliter of medium. Thus, gentamicin levels sufficient to inhibit the growth of sensitive bacteria were still present in the donor cornea three hours and in the iris two hours after penetrating keratoplasty. By six hours, only trace amounts of gentamicin were found in the donor cornea and aqueous humor. The presence of gentamicin in ocular tissues after penetrating keratoplasty appears to prolong the antibacterial effect of the preserving medium, and to provide tissue concentrations of antibiotic effective against intraoperative contamination.