Drug-loaded nanocarriers for back-of-the-eye diseases- formulation limitations

The main therapeutic advances in ophthalmology have been made in diseases affecting the posterior eye segment that are presently increasing and can lead to partial or complete blindness if untreated. Therapy is based on efficient hydrophilic macromolecules which can only be injected in the vitreous every month. However, frequent intravitreal injections have been associated with injection-related adverse events such as retinal detachment and endophthalmitis. Many intravitreal formulations based on liposomes, nanoemulsions and nanoparticles have been proposed to sustain drug release for a prolonged period of time, thereby alleviating repeated injections which otherwise exacerbate the clinical condition. Despite extensive efforts and significant investments, there is still no nanodelivery system in clinical trials even in the early stages for such a purpose. We will focus on three major obstacles; the limitation of the drug dose imposed by the small volume required to be injected in the vitreous (50 μl), the drug loading capacity of the nanocarriers, and the complexity of the industrial production of the nanocarriers. New therapies have appeared but there is still a lot of room for improvement as several unmet medical needs prevail and need to be addressed in order to ameliorate efficacy, safety and usability of these treatments.