Iontophoretic Therapies in Ophthalmology

Table 2 provides a list of the drugs, dyes, and other charged molecules summarized below. The cations (positive ions) are used in anodal (positive electrode) iontophoresis, whereas the anions (negative ions) are used in cathodal (negative electrode) iontophoresis. Iontophoresis of the various classes of drugs (antibiotics, antivirals, antifungal, antimetabolite, adrenergic, steroid, anesthetic, and dyes) can be delivered by two approaches. Transcorneal iontophoresis (described earlier and in diagrammatic form in Fig. 1) delivers a high concentration of drug to the anterior segment of the eye (cornea, aqueous humor, ciliary body, and lens). In phakic animals, the lens-iris diaphragm limits penetration of a drug to the posterior tissues of the eye such as posterior vitreous and retina. This barrier can be overcome by applying the current through the pars plana (transscleral iontophoresis), which can produce significantly high and sustained drug concentration in the vitreous and retina. For transscleral iontophoresis, the drug solution is contained in a narrow tube within an eyecup held to the conjunctiva by suction. The tube is placed over the pars plana to avoid current damage to the retina. This technique circumvents the lens-iris barrier and delivers drugs into the vitreous or retina. Figure 2 shows a diagram of a transscleral iontophoresis device and setup.

Within the past 10 years, a number of excellent articles/chapters have reviewed the application of iontophoresis in therapeutic approaches in ophthalmology (11,12,42-44). Current research in ocular iontophoresis is aimed at resolving the delivery problems associated with newly developed

Table 2 Drugs Used in Ocular Iontophoresis

Class

Drug

Site

Ion

Application

Ref.

Antibiotic

Gentamicin

Transcorneal

Cation

Tx Pseudomonal keratitis

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