Abstract
Nanoemulsions are considered as the most promising solution to improve the delivery of ophthalmic drugs. The design of ophthalmic nanoemulsions requires an extensive understanding of pharmaceutical as well as technological aspects related to the selection of excipients and formulation processes. This Review aims at providing the readers with a comprehensive summary of possible compositions of nanoemulsions, methods for their formulation (both laboratory and industrial), and differences between technological approaches, along with an extensive outline of the research methods enabling the confirmation of in vitro properties, pharmaceutical performance, and biological activity of the obtained product. The composition of the formulation has a major influence on the properties of the final product obtained with low-energy emulsification methods. Increasing interest in high-energy emulsification methods is a consequence of their scalability important from the industrial perspective. Considering the high-energy emulsification methods, both the composition and conditions of the process (e.g., device power level, pressure, temperature, homogenization time, or number of cycles) are important for the properties and stability of nanoemulsions. It is advisible to determine the effect of each parameter on the quality of the product to establish the optimal process parameters’ range which, in turn, results in a more reproducible and efficient production.
Highlights
Ophthalmic therapy is largely based on topical administration of aqueous active pharmaceutical ingredients (API) solutions which are eliminated shortly after instillation by the nasolacrimal drainage system.[1,2] The short residence time of the conventional ocular formulations in the conjunctival sac is limiting drug penetration into the deeper layers of the eye to less than 5% of the administered dose,[3] while other reports indicate that the effectively absorbed ocular dose is smaller than 1% of the instilled dose.[4]
Optical microscopy may provide some insight into structural characteristics of nanoemulsions, a more detailed characterization can be achieved with high-resolution electron microscopy techniques including transmission electron microscopy (TEM), cryoTEM, scanning electron microscopy (SEM), or atomic force microscopy (AFM), enabling the imaging of the dispersed particles with nanometric resolution.[69,83,87]
Between 2015 and 2018 there was an 800% increase in approvals of new ophthalmic drugs including topical treatments.[118−120] manufacturers are increasingly investing in research and development of innovative, noninvasive ophthalmic preparations, there is still a significant unmet need for the availability of multiactive ophthalmic drug formulations, including combination therapy products
Summary
Ophthalmic therapy is largely based on topical administration of aqueous active pharmaceutical ingredients (API) solutions which are eliminated shortly after instillation by the nasolacrimal drainage system.[1,2] The short residence time of the conventional ocular formulations (i.e., eye drops) in the conjunctival sac is limiting drug penetration into the deeper layers of the eye to less than 5% of the administered dose,[3] while other reports indicate that the effectively absorbed ocular dose is smaller than 1% of the instilled dose.[4]. Marketed ophthalmic nanosize drug delivery systems include micelles (Cequa), liposomes (VISUDYNE, Lacrisek, Artelac Rebalance), and nanoemulsions (Restasis, Cyclokat, Ikervis, Durezol, Xelpros, Systane Complete).[7,10−13] Several nanoemulsions were in advanced clinical evaluation
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