In ophthalmology, ensuring the effective delivery of therapeutics is crucial. Intensive research and development efforts are consistently expanding the possibilities beyond the limits set by traditional topical formulations. Throughout history, solutions and suspensions like eye drops have been the predominant treatment method, standing the test of time. Similarly, most ophthalmic drugs are applied topically, with the rest administered systemically. As per Inkwood Research, the global ophthalmic drugs market is expected to project a CAGR of 6.09% and reach a revenue of $66508.62 million by 2032.
Furthermore, the prevailing approach involves the application of non-invasive, topically applied drugs. However, given the paramount importance of vision for evolutionary survival, the eye has evolved mechanisms to prevent foreign materials from breaching its protective barriers. Consequently, any drug-delivery mechanism must adeptly administer medication without causing lasting impairment to these vital barriers.
The examination of the rates at which drugs traverse or engage with various ocular barriers holds considerable importance in ocular drug administration. Simultaneously, the appeal of topical ophthalmic drugs stems from their convenient administration, non-invasive characteristics, and the capability to target the specific site of action. These qualities render them appealing for the treatment of diverse eye conditions, including but not limited to conjunctivitis, glaucoma, and dry eye.
However, this blog examines the barriers to topical ocular drug delivery.
Ophthalmic Drugs Market: Challenges to Topical Ocular Drug Delivery
Patient Compliance
Achieving patient adherence poses a significant challenge in topical drop administration, as indicated by substantial evidence pointing to a considerable proportion of patients experiencing prolonged periods of inadequate drug concentration levels. Variability in the volume of instilled doses further complicates the situation, influenced by factors such as the force applied during squeezing, the angle of administration, and the ability to resist blinking. Additionally, research has demonstrated a linear increase in tear drainage rate corresponding to the instilled volume.
Consequently, Dr. Gregg J. Berdy, a medical professional affiliated with Ophthalmology Associates of St. Louis, Missouri, and serving as a voluntary associate professor of clinical ophthalmology in the Department of Ophthalmology at Washington University School of Medicine, asserts that physicians commonly favor intraocular injectable drugs for in-office administration. The appeal lies in the assurance of precise dosing with these medications. Injectable treatments typically adhere to a schedule ranging from every three months to a year, sparing patients the concern of monthly prescription refills over an extended period. Additionally, the risk of inadvertent harm to the ocular surface during the application of topical solutions is eliminated.
In light of the advantages and drawbacks associated with topicals, it comes as no surprise that significant research has been directed toward the development of topical ophthalmic drug products that offer enhanced user-friendliness, increased comfort, and a reduction in administration frequency. These endeavours encompass the creation of sustained or extended-release formulations and efforts to enhance the bioavailability of active drug substances.
Natural Barriers
The need for frequent dosing of topical ophthalmic drugs stems from the fact that, typically, only about 5% of the administered drug substance in a standard eye drop is absorbed at the intended site of action. This issue is primarily attributed to the complex path that a drug must traverse to effectively penetrate the target tissue.
While the average eye drop volume is 40–50 μL, the eye’s tear film capacity is a mere 7 μL, and its total holding capacity is approximately 20–25 μL. This mismatch leads to considerable product wastage and poses a significant constraint on effective drug delivery. Moreover, the residual liquid is susceptible to natural drainage and blinking, making it difficult to retain a topical drug product in place long enough for absorption.
Considering the formidable protective barriers and mechanisms present on the ocular surface, achieving relevant drug concentrations in different parts of the eye becomes a formidable task. Therefore, a comprehensive understanding of the pharmacokinetics of any topical ophthalmic drug is imperative.
Accordingly, some advocate for the development of highly potent topical ophthalmic drugs tailored for treating anterior and posterior eye diseases. The key recommendation is to administer such drugs exclusively to the eye, thus circumventing systemic circulation and ensuring optimal therapeutic outcomes. (Source)
Ophthalmic Drugs Market: Future of Topical Ocular Drug Delivery
Drug-eluting contact lenses (CLs) serve as transparent corneal dressings, functioning as reservoirs for drugs and facilitating sustained drug release in close proximity to the postlens tear fluid. This innovative approach is designed for the treatment of anterior ocular disorders. Soft contact lenses loaded with drugs represent a novel drug-delivery system, not only extending and maintaining the release of drugs but also improving drug penetration through the corneal epithelium when compared to traditional eye drops.
Says Berdy, “Every major company in the ophthalmic drug sector is developing topical formulations aimed at a wide range of diseases from those more traditionally treated with drops to disorders of the posterior of the eye. They are exploring both novel compounds and new delivery technologies that will enable both greater efficacy and improved ease of use and comfort for patients.” (Source)
Accordingly, innovative product developments that address topical ocular delivery challenges will be a game-changer for the global ophthalmic drugs market.
By Akhil Nair
FAQ
Innovative drug-delivery systems, such as drug-loaded soft contact lenses, contribute significantly by extending drug release duration and enhancing corneal penetration. These systems aim to overcome the limitations associated with traditional eye drops, improving overall therapeutic outcomes.
The challenges in ophthalmic drug delivery include limited drug retention due to blinking and tear washout, low bioavailability, difficulty in reaching the target tissues, and short residence time on the ocular surface.