Increased partitioning of pilocarpine to the oily phase of submicron emulsion does not result in improved ocular bioavailability

Nanotherapies for the treatment of ocular diseases

The topical route is the most frequent and preferred way to deliver drugs to the eye. Unfortunately, the very low ocular drug bioavailability (less than 5%) associated with this modality of administration, makes the efficient treatment of several ocular diseases a significant challenge. In the last decades, it has been shown that specific nanocarriers can interact with the ocular mucosa, thereby increasing the retention time of the associated drug onto the eye, as well as its permeability across the corneal and conjunctival epithelium. In this review, we comparatively analyze the mechanism of action and specific potential of the most studied nano-drug delivery carriers. In addition, we present the success achieved until now using a number of nanotherapies for the treatment of the most prevalent ocular pathologies, such as infections, inflammation, dry eye, glaucoma, and retinopathies.

Mannosylated lipid nano-emulsions loaded with lycorine-oleic acid ionic complex for tumor cell-specific delivery

This study was to prepare a mannosylated lycorine lipid nano-emulsion formulation (M-LYC-OA-LNEs) for the aim of achieving tumor targeting delivery of lycorine (LYC) . The low lipophilicity of LYC made it hard to be dispersed into lipid nano-emulsions (LNEs). In order to increase its lipophilicity, lycorine-oleic acid ionic complex (LYC-OA) was made. M-LYC-OA-LNEs and uncoated lycorine-oleic acid loaded lipid nano-emulsions (LYC-OA-LNEs) were prepared by solvent injection method and characterized by transmission electron microscopy (TEM), particle size, polydispersity index, zeta-potential and entrapment efficiency analysis. The in vitro cellular uptake and growth inhibition activity studies were performed on A549 cell lines. The entrapment efficiency of M-LYC-OA-LNEs was 82.7 ± 1.6 %. The cellular uptake study showed that coated LNEs were preferably taken up by A549 cells than uncoated LNEs. The effective test by MTT assay showed better growth inhibition activity of M-LYC-OA-LNEs on A549 cell lines when compared with LYC-OA-LNEs and blank LNEs. These results demonstrated that M-LYC-OA-LNEs could be a promising formulation for tumor targeting delivery of LYC with the potential of being applied in the diagnosis and treatment of cancer.

Disposition of drugs in block copolymer micelle delivery systems: from discovery to recovery

Since their discovery in the early 1980s, polymeric micelles have been the subject of several studies as delivery systems that can potentially improve the therapeutic performance and modify the toxicity profile of encapsulated drugs by changing their pharmacokinetic characteristics. The efforts in this area have led in recent years to the advancement of several polymeric micellar formulations to clinical trials, some of which have shown promise in changing the biodistribution of the incorporated drug after intravenous administration as a means of tumour-targeted drug delivery. Recently, the possible benefit of polymeric micellar delivery in enhancing the absorption and bioavailability of incorporated drugs from alternative routes of drug administration has attracted interest. This article provides an overview of the effect of polymeric micellar delivery on absorption, distribution, metabolism and excretion of incorporated therapeutic agents. It also aims to assess the current information on the performance of polymeric micellar delivery systems in modifying the pharmacokinetics/pharmacodynamics of the incorporated drugs in clinical trials, and to re-examine the important structural factors required for successful design of polymeric micellar delivery systems capable of inducing favourable changes in the pharmacokinetics of the encapsulated drug.

Improvement of the Ocular Bioavailability of Carteolol by Ion Pair

Ocular bioavailability after instillation of carteolol was investigated by ion pair formation, taking into consideration a balance between lipophilicity and water solubility. The octanol/ water partition coefficient (PC(O/W)) and the aqueous humor concentration in rabbits after instillation of carteolol containing fatty acids having not more than 6 carbons were measured. The longer carbon chain fatty acid showed the higher PC(O/W) of carteolol. The aqueous humor concentration of carteolol increased with carbon chain length of fatty acid and was clearly correlated with logPC(O/W). The increment of counter ion also increased both the logPC(O/W) and aqueous humor concentration of carteolol. The findings suggested that the transcorneal absorption of carteolol would be designed by coordinating with quality and quantity of counter ions. The area under concentration (AUC) in aqueous humor applied by ion pair formulation containing 2% carteolol with sorbate was 2.6 times higher than that by 2% carteolol ophthalmic solution (control), whereas the AUC applied by 4% carteolol ophthalmic solution was 1.4 times higher. The plasma level after instillation of ion pair formulation was almost the same as that of 2% ophthalmic solution. The ratio of AUC (aqueous humor/ plasma) of ion pair formulation was markedly higher, as compared with those of 2% and 4% ophthalmic solution. These results showed that the ion pair formation with sorbate improved the ocular bioavailability of carteolol without enhancing systemic absorption.

The potential of lipid emulsion for ocular delivery of lipophilic drugs

For nearly a decade, oil-in-water lipid emulsions containing either anionic or cationic droplets have been recognized as an interesting and promising ocular topical delivery vehicle for lipophilic drugs. The aim of this review is to present the potential of lipid emulsions for ocular delivery of lipophilic drugs. The review covers an update on the state of the art of incorporating the lipophilic drugs, a brief description concerning the components and the classification of lipid emulsions. The ocular fate following topical instillation, safety evaluation experiments and the applications of lipid emulsions are thoroughly discussed.

Cyclosporine A delivery to the eye: a pharmaceutical challenge

Systemic administration of cyclosporine A (CsA) is commonly used in the treatment of local ophthalmic conditions involving cytokines, such as corneal graft rejection, autoimmune uveitis and dry eye syndrome. Local administration is expected to avoid the various side effects associated with systemic delivery. However, the currently available systems using oils to deliver CsA topically are poorly tolerated and provide a low bioavailability. These difficulties may be overcome through formulations aimed at improving CsA water solubility (e.g. cyclodextrins), or those designed to facilitate tissue drug penetration using penetration enhancers. The use of colloidal carriers (micelles, emulsions, liposomes and nanoparticles) as well as the approach using hydrosoluble prodrugs of CsA have shown promising results. Solid devices such as shields and particles of collagen have been investigated to enhance retention time on the eye surface. Some of these topical formulations have shown efficacy in the treatment of extraocular diseases but were inefficient at reaching intraocular targets. Microspheres, implants and liposomes have been developed to be directly administered subconjunctivally or intravitreally in order to enhance CsA concentration in the vitreous. Although progress has been made, there is still room for improvement in CsA ocular application, as none of these formulations is ideal.