Ocular drug delivery through ophthalmic lenses (OLs) has been investigated in the last decades as an alternative to the commonly used eye drops. One of the main advantages of using therapeutic OLs is that they allow achieving a more controlled release than the eye drops. More, drugs delivered through topical application present a short residence time in the tear film, leading to a low drug bioavailability (< 5%), whereas, therapeutic OLs may increase the ocular residence time of drugs, minimizing drug waste and side effects.
In this work, a mathematical description of the diffusion-based release mechanism of a drug from an OL material is described: 1) from a single poly(2-hydroxyethylmethacrylate) (PHEMA) based lens and 2) from a multi-layer PHEMA lens (3 layers), where only the inner layer is drug loaded. Diffusivity of the studied model drugs (levofloxacin and chlorhexidine) and a mass transfer related parameter are obtained through the fitting of the mathematical numeric solutions to experimental drug release results. The numerical results here obtained are compared with those obtained with a general analytic solution for the same diffusion-based process.
It is shown that the proper combination of materials with adequate drug diffusivity, thicknesses and interfacial transport characteristics allows for the control of the drug delivery from multi-layered ophthalmic lenses, such that drug bursts can be minimized, and the release time can be optimized.