Ocular drug delivery: A comparison of transcorneal iontophoresis to corneal collagen shields

Abstract

Topical administration of drugs to treat ocular disease is accomplished primarily by means of solutions, ointments, and suspensions. These are relatively inefficient as drug delivery systems; often only 1% of the available drug is absorbed by the eye. Two ocular drug delivery systems currently being studied are transcorneal iontophoresis and collagen shields. Transcorneal iontophoresis is intended to drive charged drugs by an electric current into the cornea. In a Pseudomonas model of bacterial keratitis, as well as in pharmacokinetic studies, ocular iontophoresis of gentamicin, tobramycin, or ciprofloxacin was superior to topical ocular drops for reducing Pseudomonas in the cornea. Both iontophoretic methods were shown to be safe and nontoxic to the rabbit corneal epithelium. The collagen shield, designed to prolong drug contact with the eye, is made from porcine scleral tissue that has been extracted and molded into a contact lens configuration. The shields can absorb the equivalent of drug present in 1–2 drops of a topical aqueous solution. Chemotherapeutic studies in an experimental Pseudomonas keratitis model showed that collagen shields containing gentamicin, tobramycin, or ciprofloxacin were equal to or better than frequent applications of fortified antibiotic drops for significantly reducing the bacteria in the cornea. The results gained from these experimental studies on corneal iontophoresis suggest the need for clinical trials.