Transscleral iontophoresis

M. Barza, C. Peckman, and J. Baum. Transscleral iontophoresis of cefazolin, ticarcillin, and gentamicin in the rabbit. Ophthalmology 93 133-139 (1986)... 

Li et al. [196] studied the sites of ion delivery in the eye during iontophoresis. Using nuclear magnetic resonance imaging (MRI) and a probe ion (Mn2+), the study compared transscleral with transcorneal iontophoresis. The results have shown that transscleral iontophoresis delivered the ion into the vitreous, whereas transcorneal iontophoresis delivered the ion into the... 

Grossman, R.E., D.F. Chu, and D.A. Lee. 1990. Regional ocular gentamicin levels after transcorneal and transscleral iontophoresis. Invest Ophthalmol Vis Sci 31 909. 

Vollmer, D.L., et al. 2002. In vivo transscleral iontophoresis of amikacin to rabbit eyes. J Ocul... 

FIGURE 26.6 Annular-shaped silicone probe for transscleral iontophoresis (Eyegate, Optis) applied on the eye. Used by Behar-Cohen et al. [38], Hayden et al. [39], and Voigt et al. [40]. (Adapted from Behar-Cohen, F.F. et al., Exp. Eye. Res., 74, 51, 2002. With permission.)... 

A polyacrylic-porous hydrogel saturated with gentamicin or dexamethasone solutions for transcorneal and transscleral iontophoresis has been reported [56 59]. A battery-operated portable device that applies a variable electrical current up to 1 mA, for preset periods of time is used (Figure 26.8). Hydrogels are prepared by radical polymerization of an aqueous... 

A number of antibiotics, including gentamicin, cephazolin, ticarcillin, amikacin, and vancomycin have been successfully delivered into the vitreous of rabbit eyes (Table 26.2). Barza et al. [74] further investigated the efficacy of transscleral iontophoresis of gentamicin for the treatment of Pseudomonas endophthalmitis in rabbits. They found that two sessions of iontophoresis in addition to an intravitreal injection of gentamicin resulted in a significantly lower number of bacterial colonies in the vitreous than by the injection alone. 

Transscleral iontophoresis of steroids (dexamethasone and methylprednisolone) can be an alternative treatment for many ocular inflammations. Lam et al. [36] demonstrated high... 

FIGURE 26.11 Illustration of drug distribution to posterior segments of the eye after transscleral iontophoresis. (Adapted from Hastings, M.S. et al., Drug Deliv. Tech., 4, 53, 2004. With permission.)... 

The direct influence of the current density and the iontophoretic time period on the drug levels achieved in posterior eye segments was demonstrated after transscleral iontophoresis of amikacin [54], gentamicin [37], and methylprednisolone [38] (Table 26.2). 

Detailed pharmacokinetic studies were performed on transscleral iontophoresis of various drugs [38-40,42,75-78]. Each drug resulted in different patterns of distribution in the vitreous. Carboplatin distribution in the vitreous after iontophoretic delivery demonstrated heightened levels in a controlled manner from 1 to 6 h after treatment [39], Foscarnet iontophoresis demonstrated a very low elimination rate, thus therapeutic levels in the vitreous were maintained for up to 60 h [78]. Methylprednisolone obtained a relatively low peak concentration 2 h after treatment [38], and gentamicin showed a peak concentration 16 h after the transscleral iontophoresis [42]. 

Transscleral Iontophoresis of Drugs into Rabbit Eyes... 

Transcorneal and transscleral iontophoresis, at the same conditions, can produce different toxicity levels due to the significant differences between cornea tissue and sclera. Any damage to the corneal surface immediately affects the vision and comfort of the patient, which is less pronounced when applied to the sclera. The clarity of the cornea is essential for interaction with light whereas the sclera is not relevant for light interaction. The cornea is an avascular and highly innervated tissue, unlike the sclera, and thus very sensitive to pain and hypoxia. On one hand, transcorneal iontophoresis endangers the front window of the eye, but on the other hand transscleral iontophoresis threatens the retina underneath the application site, which is essential for visual image formation. 

Eljarrat-Binstock, E., et al. 2005. Transcorneal and transscleral iontophoresis of dexamethasone phosphate in rabbits using drug loaded hydrogel. J Control Release 106 386. 

Chauvaud, D., et al. 2000. Transscleral iontophoresis of cortcicosteoids Phase II clinical trial. Invest Ophthalmol Vis Sci 41 S79. 

Yoshizumi, M.O., et al. 1991. Experimental transscleral iontophoresis of ciprofloxacin. J Ocul Pharmacol 7 163. 

---