Transscleral iontophoresis of cefazolin, ticarcillin, and gentamicin in the rabbit

Corneal iontophoresis produces high concentrations of drugs in the anterior segment but not in the vitreous humor of the phakic eye, presumably because transport is impeded by the lens-iris barrier. We have used two modifications to produce high levels of commonly used antibiotics in the vitreous humor of the phakic rabbit eye: the device is placed over the pars plana, circumventing the lens-iris barrier; the contact area of the column of fluid is kept small (less than or equal to 1 mm diameter) so as to provide a high current density. Applying 2 mAmp for 10 minutes, we were able to achieve mean vitreal concentrations of cefazolin, ticarcillin, and gentamicin of 94-207 micrograms/ml in the normal rabbit eye. Drug penetration showed a correlation with strength of current (0.1-2 mAmp) and with duration of iontophoresis (1-10 minutes) but not with concentration of the drug solution. Transscleral iontophoresis is a promising noninvasive technique to achieve high vitreal levels of charged solutes.