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Sarah Molokhia, Kongnara Papangkorn, Charlotte Butler, Donald Mix, John Higuchi, Balbir Brar, S Kevin Li, William Higuchi; The Influence of Formulation Factors on Transscleral Iontophoretic Delivery of a Macromolecule in Vitro and in Vivo. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3204.
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To study the effects of ionic strength and pH on the transscleral anodal iontophoresis (AI) delivery of Immunoglobulin G (IgG) and to evaluate these effects on the amount and distribution of IgG delivered into the rabbit eye.
IgG formulations (MW~150 kDa, a surrogate for bevacizumab) of different ionic strengths and pH were investigated in vitro (n=3 per group). In vitro AI experiments were conducted with conjunctiva + sclera membranes of New Zealand white (NZW) rabbits in a side-by-side diffusion cell with the IgG formulation in the donor chamber and PBS in the receiver chamber. Silver and silver chloride electrodes were used as the conductive elements for the iontophoresis experiments. For the in vivo experiments, an iontophoretic applicator (Visulex-I) was applied on the rabbit eye under optimized formulation conditions. After 20 minutes of 4 mA AI delivery, the rabbits were sacrificed and the eyes enucleated. The eyes were dissected into cornea, anterior chamber, vitreous, conjunctiva, sclera and choroid/retina and the tissues were analyzed for IgG content by ELISA.
The in vitro permeability coefficient (P) value determined for conjunctiva+sclera membrane increased approximately 2.7 fold when decreasing the formulation ionic strength by approximately 13 fold of a prior formulation. This corresponds to a 2.7 fold increase in total amount delivered across the membrane. A decrease in the formulation pH from 6.5 to 2.5 resulted in a 40 fold decrease of the P value. An increase in the total amount of IgG delivered in vivo was also observed at the lower ionic strength. The total amount of IgG delivered in vivo into the eye and into the retina/choroid with our optimized low ionic strength formulation was approximately 302.2 ± 30.0 μg and 5.2 ± 2.4 μg, respectively. The retina/choroid amount is of the same order of magnitude of levels delivered to the retina/choroid from an IVT injection of bevacizumab in rabbits (literature reported Cmax value of 94 μg/g, which is approximately 15 μg).
Electroosmosis can be compromised by a low pH but can be enhanced by utilizing a low formulation ionic strength. An optimized Visulex-I applicator and formulation can be expected to deliver to the eye a therapeutically relevant dose of an antibody/macromolecule such as Avastin.
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