Transscleral iontophoresis of dexamethasone
T. T. Lam, D. P. Edward, X. A. Zhu and M. O. Tso
Department of Ophthalmology, University of Illinois, Chicago 60612.
Transscleral iontophoresis has been suggested to be a potentially useful
noninvasive technique in intravitreal introduction of ionizable drugs, such
as cefazolin sodium, ticarcillin disodium, and gentamicin sulfate. To
investigate the usefulness of this technique in the administration of
corticosteroids, we performed transscleral iontophoresis of dexamethasone
sodium phosphate (300 mg/mL, 20 mmol/L edetic acid [EDTA]) into rabbits at
a current of 1.6 mA for 25 minutes. Eyes were enucleated at different time
intervals and frozen in liquid nitrogen. The frozen vitreous bodies and
adherent sensory retina were collected and sonicated, and dexamethasone
levels were measured using high-pressure liquid chromatography. In
addition, to study the facilitation of drug transport by cryotherapy, a
second group of rabbits were given a single application of cryotherapy (-78
degrees C, 45 seconds) 3, 7, and 14 days before iontophoresis in the same
region. Without cryotherapy, the initial level of dexamethasone in the
vitreous body-sensory retina after iontophoresis was 139.3 +/- 51.5 mg/L
(mean +/- SE) (n = 6) with a half-life of less than 2 hours. In the
cryotreated group, the levels of dexamethasone immediately after
iontophoresis 3, 7, and 14 days after cryotherapy were 61.5 +/- 31.7 (n =
6), 88.4 +/- 55.1 (n = 6), and 112.2 +/- 32.5 (n = 6) mg/L, respectively,
indicating that levels were lower compared with the group without
cryotherapy. Our results suggest that a high dose of dexamethasone can be
delivered by using this noninvasive technique and that cryotherapy before
iontophoresis does not increase drug levels in the vitreous body.
