Enhancement of the ocular bioavailability of topical tobramycin with use of a collagen shield.

We compared the ocular bioavailability in rabbits of 0.3% tobramycin applied with a collagen shield with eyedrop tobramycin application. Groups of rabbits received either (1) a collagen shield presoaked in tobramycin with a tobramycin drop before and after shield application (Shield) or (2) three drops of tobramycin (Drops). Postmortem samples of the cornea, conjunctiva, and aqueous humor were obtained at various intervals after shield application or drop instillation. The corneas in a second set of rabbits were anesthetized and then chemically abraded with n-heptanol before receiving the same two dosing regimens as in the groups with intact corneas. At nearly all times in all three tissues, the Shield groups had higher mean concentrations of tobramycin than the Drops groups. The area under the concentration-time curve for the Shield group relative to the Drops group was 5.0- to 16.1-fold greater for rabbits with intact corneas (P < .05), and 1.8- to 3.7-fold greater for rabbits with abraded corneas (P < .05). The use of collagen shields together with standard ophthalmic concentrations of tobramycin may be useful in achieving higher concentrations of topically delivered drugs into the anterior segment of the eye.