Regional ocular gentamicin levels after transcorneal and transscleral iontophoresis.

Abstract

Transcorneal and transscleral iontophoresis were compared to subconjunctival injection (control) in the delivery of gentamicin into rabbit eyes. Gentamicin levels in the corena, aqueous, and vitreous were measured by a fluorescence polarization assay at various time intervals after treatment. A mean peak corneal concentration of 376.1 micrograms/ml was achieved 2 hr after transcorneal iontophoresis. This was significantly higher than the level obtained in control eyes (P = 0.016). A mean peak aqueous humor concentration of 54.8 micrograms/ml occurred 2 hr after transcorneal iontophoresis. This was significantly higher than the peak level of 14.2 micrograms/ml after subconjunctival injection (P = 0.003). Inhibitory levels (approximately 5 micrograms/ml) were maintained in both aqueous and cornea for 8 hr after transcorneal iontophoresis. After transscleral iontophoresis, the mean peak vitreous humor concentration was 53.4 micrograms/ml at 16 hr and remained inhibitory through 24 hr; the peak aqueous level was 23.2 micrograms/ml and remained inhibitory for 24 hr. Peak drug concentrations in the vitreous were significantly higher than control (P = 0.026). Therapeutic vitreous humor levels were not achievable after transcorneal iontophoresis or subconjunctival injection. Potential corneal toxicity of transcorneal iontophoresis was demonstrated by measuring corneal thickness and endothelial cell counts prior to and 3 days after transcorneal iontophoresis of gentamicin and balanced saline solution (BSS) (control). No significant differences existed between eyes treated with gentamicin compared to those treated with BSS or when pre- versus postiontophoresis of gentamicin in the same eyes were compared. Transcorneal and transscleral iontophoresis may be an effective noninvasive method of delivering inhibitory levels of gentamicin to the cornea, aqueous humor, and vitreous for the treatment of intraocular infections.