Drug delivery to the eye has always been a challenge due to the presence of various anatomical and physiological barriers, and until recently almost the only options were eye drops, ointments, and intravitreal injections. Is such application still acceptable or should we resort to some other approaches? You can read more about innovations in drug delivery to the eye below.
What do we want?
The ideal drug delivery to the eye should include increased bioavailability of the drug, controlled release of the drug and its prolonged retention at the site of action while reducing the frequency of dosing and, of course, without damaging the eye. In this way, even with local therapy, the systemic effects of the drug can be avoided or at least reduced, especially in chronic use.
Today and tomorrow
Conventional ophthalmic therapy involves the use of topical eye drops and intravitreal injections to treat disorders of the anterior and posterior segment of the eye. Until recently, drug delivery to the posterior segment of the eye took the form of uncomfortable intravitreal injections, which led to the need to develop new, more effective, and more acceptable therapeutic systems. Pharmaceutical technology continuously discovers various state-of-the-art inventions for continuous and controlled drug delivery. Nanomicels, nanoparticles, ocular inserts, tear duct “plugs”, eye implants, contact lenses and ocular iontophoresis are just some of them.
Pathological eye disorders are divided into anterior and posterior segment disorders. Anterior segment disorders, such as dry eye, glaucoma, and allergic conjunctivitis, are generally successfully treated today with conventional eye drops and ointments. The main disadvantage of this drug administration is the low bioavailability which can be attributed to several static (eye anatomy) and dynamic (blinking, continuous tear fluid circulation and nasolacrimal drainage) barriers to successful absorption. Nevertheless, it is still the best-accepted therapy for the treatment of anterior segment disorders. On the other hand, disorders of the posterior segment of the eye very often result in loss of vision due to damage to the retina. One of the complications of hyperglycemia, i.e. diabetes, is damage to retinal endothelial cells that causes disorders known as diabetic retinopathy, diabetic macular oedema, and retinal vein occlusion. At the same time, other parts of the eye suffer, so diabetic keratinopathy is common. Conventional therapy for posterior segment disease is the use of intravitreal injections that are invasive and can cause intraocular inflammation, retinal damage, and bleeding. Due to the unacceptability of such invasive drug routes, and the increased incidence of diabetes complications, there is an urgent need to develop new, non-invasive drug delivery systems that will overcome eye barriers, release the drug in a controlled manner, and maintain effective levels in the back of the eye.
Drug-releasing contact lenses are transparent corneal coatings made of polymer hydrogels that act as reservoirs for the drug and release it at the stimulation of tear fluid. This method of drug delivery is innovative that not only controls drug release, but also increases drug penetration through the corneal epithelium, but also prolongs drug-eye contact. Some studies show that contact lenses offer the highest bioavailability of the drug compared to other noninvasive ophthalmic systems, and also provide a significant dosing advantage over frequent and not always accurate dosing of eye drops ( 1,2,4). In addition, the advantage of the lenses is their ease of use and suitability for long-term therapy due to their excellent biocompatibility and comfort, and continuous drug delivery at the same time. For lenses to be suitable as a therapeutic system, they must be transparent, oxygen-permeable (because most of the exchange of gases for the eye takes place over its surface exposed to air) and adequate humidity. There are different methods by which drugs are incorporated into polymer lenses: molecular injection, particle loading, use of vitamin E and cyclodextrin, and impregnation with supercritical fluids ( 2).
Today, primarily this method of drug delivery is being investigated for the treatment of anterior eye disease, but there is also research on this application for the therapy of the posterior segment ( 3). This leaves us with the hope that in the future, the very unpleasant consequences of diabetes complications, such as visual impairment, will be able to be treated successfully and non-invasively locally.
Translated by: Ines Jurak
2 Singh K et al. Novel Approaches in Formulation and Drug Delivery using Contact Lenses. J Basic Clin Pharm, 2011, 2 (2), 87-101.
3 Alvarez-Rivera F, Concheiro A, Alvarez-Lorenzo C. Epalrestat-loaded silicone hydrogels as contact lenses to address diabetic-eye complications. Eur J Pharm Biopharm, 2018, 122, 126-136
4 Ako-Adounvo AM et al. Recent Patents on Ophthalmic Nanoformulations and Therapeutic Implications. Recent Pat Drug Deliv Formul, 2014, 8 (3), 193-201