Insights to Using Contact Lenses for Drug Delivery

There has been considerable interest in the potential application of contact lenses for ocular drug delivery. This short communication provides an overview of the challenges faced by delivering drugs using contact lenses, highlights the solutions to limitations that have already been achieved, and describes the barriers that remain before commercial application can be realized. *Corresponding author: Chau-Minh Phan, Centre for Contact Lens Research, School of Optometry and Vision Science, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada, Tel: +1 519 8884567; E-mail: [email protected] Received October 30, 2013; Accepted December 26, 2013; Published January 02, 2014 Citation: Phan CM, Hui A, Subbaraman L, Jones L (2014) Insights to Using Contact Lenses for Drug Delivery. Clin Exp Pharmacol 3: 145. doi:10.4172/21611459.1000145 Copyright: © 2014 Phan CM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Introduction In the last few decades, potential applications of Contact Lenses (CL) beyond their use to correct refractive error have been investigated, including extensive research towards their use for ocular drug delivery. At present, topical eye drops remain the most common method for treating ocular disease, accounting for 90% of all ophthalmic formulations [1-4] and they are readily accepted by patients due to their convenience and cost effectiveness [1]. However, the ocular anatomy presents several barriers that prevent the effective and efficient delivery of medication from eye drops, including continuous tear dilution [5-7], dispersion and drainage during blinking and tear flow [5,7,8], non-specific absorption [1,5,7], and variable drug penetration [4]. This results in only 1-7% of the medication within an eye drop reaching the target tissue and exerting a therapeutic effect [8], with the remainder being either spilled onto the external ocular surface or absorbed systemically [9]. High turnover and poor absorption leads to the need for multiple dosing over extended periods to achieve therapeutic drug concentrations, leading to problems relating to patient compliance [10,11], as well as the potential for drug overdosing [12]. These limitations suggest that there is considerable room for improvement if efficient and effective treatment of anterior segment diseases is to occur. Contact lenses are often used in cases of ocular trauma or postsurgery as so-called ‘bandage lenses’, as a means to manage pain and promote re-epithelialization [13]. Several commercially available CLs, including Pure Vision (balafilcon A, Bausch+Lomb), Acuvue 2 (etafilcon A, Vistakon Inc.), Acuvue Oasys (senofilcon A, Vistakon Inc.), and Air Optix Night & Day (lotrafilcon A, Alcon) are FDA approved for use as bandage lenses [13-19]. In most cases, antibiotics and anti-inflammatory drugs are administered in conjunction with the CLs by adding the medication topically over the lens in situ [13,20]. This practice, although simple, is cumbersome and may not provide the desired effectiveness, with the uptake and release of the drug during such a process being unknown and uncontrolled. A survey of ophthalmic practitioners across the United States and Canada revealed that there is a strong interest in a CL that is specifically developed for use as a drug delivering therapeutic CL and that such a product would be well received by practitioners [13]. Advantages of using Contact Lenses The use of CLs for ocular drug delivery overcomes several of the barriers that limit the effective use of eye drops. The placement of a CL on the cornea separates the tear film into pre-lens (exposed to the external environment) and post-lens (between the lens and cornea) compartments, with the post-lens compartment being of particular interest due to limited tear mixing and exchange [21,22]. As a result, drugs released from the CL into this compartment potentially have a prolonged contact time with the cornea, leading to improved bioavailability [23]. Over 50% of the drugs released from a CL can diffuse into the cornea, which is at least 35 times more efficient than eye drops [24]. This increase in efficiency permits substantially reduced concentrations to be used, decreasing the potential for side effects as less drug is absorbed systemically. Another advantage to using a CL as a drug delivery platform is the ability to deliver drugs over extended time periods, which eliminates the need for multiple dosing. For ocular infections such as microbial keratitis, eye drop applications can be as frequent as applications every hour [25]. This can be very difficult for patients, especially during sleep, and severe infections often lead to hospitalization, purely to ensure appropriate drug administration [10,11]. Contact lenses effectively serve as a drug reservoir and release the drug over a set time period. In an ideal situation, the target drug forms an interaction with the CL polymer, and dissociates from the lens network in a time-dependent manner into the post-lens tear film, for eventual absorption by the ocular tissues. Past Barriers Contact Lenses Coming of Age It is somewhat surprising that although the potential application of CLs for ocular drug delivery was suggested in the 1960s [26,27], there continues to be no commercial products available. The initial problem with this concept was that early Conventional Hydrogel (CH) CLs did not provide adequate oxygen transmission to the cornea, resulting in hypoxia-related complications during overnight wear, limiting their long term therapeutic potential [28,29]. This issue was eventually overcome in the late 1990s, when highly oxygen permeable Silicone Hydrogel (SH) CLs were introduced. These lenses permitted nearnormal corneal physiology during extended periods of wear [30,31], and the idea of CLs for drug delivery became all the more promising, with this significant hypoxic hurdle seemingly solved. Aside from oxygen delivery issues, the use of CLs for drug delivery also has another major obstacle. Simple drug loading methods, such as soaking a commercial CL in pharmaceutical preparations inevitably leads to rapid release kinetics [32]. While different CL material and drug combinations provide different release durations, the overall Citation: Phan CM, Hui A, Subbaraman L, Jones L (2014) Insights to Using Contact Lenses for Drug Delivery. Clin Exp Pharmacol 3: 145. doi:10.4172/2161-1459.1000145