Trans-scleral iontophoresis of gentamicin.

Bactericidal levels of gentamicin were obtained in vitreous humor by iontophoresis of antibiotic directly through the sclera. A silicone rubber tube of small diameter filled with gentamicin sulfate formed the electrode. A two milliampere current applied for three minutes to each of four perilimbal sites introduced gentamicin sufficient to maintain therapeutic levels for more than 24 hours. The proportion of drug reaching vitreous versus aqueous humor was dependent on electrode position relative to retina and pars plana. An endogenous antibacterial agent was apparently released during iontophoretic stimulation and interfered with the bacterial growth inhibition assay. Ketoconazole, a water-insoluble antifungal agent, has also been introduced successfully into vitreous humor by anodal iontophoresis after protonation in weak acid.