Effect of the surface layer on drug release from delefilcon-A (Dailies Total1®) contact lenses
Contact lenses are receiving significant attention for delivering ophthalmic drugs with higher bioavailability compared to eye drops. Here we explore drug transport from delefilcon-A Dailies Total1® lenses which are designed to have a thin, high-water content layer on the surface. Our goal is to determine the impact of this high water content layer on drug transport for both hydrophobic (dexamethasone and cyclosporine) and hydrophilic (timolol and levofloxacin) drugs. Drugs were loaded into the lens by soaking in aqueous drug solutions till equilibrium, followed by release in phosphate buffered saline. The concentration data during release was fitted to the diffusion equation without considering the surface layer. If fits were poor, the surface layer was include in the model, as a burst release. Results showed that surface layer resulted in a burst release of about 35% of the loaded drug for the two hydrophilic drugs, and the model did not fit the data unless the surface layer was incorporated as a burst release. For the hydrophobic drugs, there was no burst release and the model fitted the data without including the surface layer likely because of the low partition coefficient of the hydrophobic drugs in the surface layer compared to the lens. The results further confirm the presence of the high water content surface layer on the Dailies Total1® lenses. The release profile of the burst release for hydrophilic drugs could be therapeutically useful for antibiotics where a high dose is desirable initially. The effect of vitamin E loading—an established procedure for increasing drug release time in other commercial lenses, was also tested on the release of timolol maleate and levofloxacin. A 20% vitamin E loading was found to increase the release time of timolol and levofloxacin by a factor of 5 and 3-fold respectively, but this increase proved much less effective compared to vitamin E’s effect on other commercial silicone hydrogels.