Photoprotection and Extended Drug Delivery by UV Blocking Contact Lenses

Extended release of photo-unstable drugs from ophthalmic inserts is not useful unless the loaded drug is protected from degradation. Because of the recent interest in extended drug delivery from contact lenses, it is critical to assess whether photo-unstable drugs can be stabilized by loading in lenses. Here, we focus on dexamethasone, which is prone to degradation and has been explored as a candidate for extended release from contact lenses for periods ranging from 10 hours to several days.

Degradation rates of dexamethasone were measured in phosphate-buffered saline and after loading in contact lenses. The degradation rates were measured in a humidified, constant-temperature (32°C) chamber with controlled UV exposure. Contact lenses with various degrees of UV blocking were used to explore the relationship between degradation rates and UV exposure. It is known that vitamin E absorbs UV radiation; thus, it was loaded into the lenses to explore the feasibility of reducing the degradation rates.

About 85% of dexamethasone degraded in 20 hours in non-UV blocking lenses, whereas less than 1% degraded in class 1 UV blocking lenses. Incorporation of vitamin E into the non-UV blocking lenses reduced the fractional degradation to 30%. Degradation rates in phosphate-buffered saline were significantly higher than even in non-UV blocking contact lenses.

The degradation of dexamethasone can be minimized by using a UV blocking contact lens or incorporating vitamin E into a non-UV blocking lens. Vitamin E incorporation has the dual benefits of improving drug stability and release profiles.