EXPLORING SIMPLE MODELS FOR DRUG DELIVERY IN OCULAR DEVICES: DIFFUSION 1D, 2D AND EFFECT OF DRUG-POLYMER BINDING

Efforts have been made to obtain new drug formulations in ophthalmologic applications to replace eye drops that are inefficient. Soft contact lenses have been using as an ophthalmic drug delivery device. Several hydrogels were used to prepare solid matrices with the drug impregnated. Assuming drug diffusion within polymeric devices as the dominant mechanism in the mass transfer process, simple models were developed to describe drug release from an ocular delivery device. The timolol maleate (medicine for glaucoma treatment) dissolution profile in the release medium for methacrylate hydrogels based contact lenses were obtained experimentally and compared with predictions considering one-dimensional and two-dimensional models. No significant differences were obtained from both predictions because the contribution of drug diffusion through radial direction in the lens is negligible, because thickness is much smaller than diameter. Although a simplistic zero-sink boundary was used to obtain the predictions, the comparison with data seems to indicate an incomplete release of the amount of timolol initially loaded into the lens. Possibly strong no reversible interactions between drug and hydrogel occur.