Cyclodextrins (CDs) are cyclic oligosaccharides (MW &lt;2500) that form hydrophilic inclusion complexes with many lipophilic and poorly soluble molecules such as drugs. The complexes are in dynamic equilibrium with free dissolved drug and CD molecules where the complexes are constantly being formed and dissembled on a milli- to micro-second time scale. In aqueous solutions CD inclusion complexes self-assemble to form transient clusters, nanoparticles (diameter between about 10 and 400 nm) and small microparticles (diameter between about 1 and 50 µm). Unlike more conventional nanoparticles formed by pure drugs or drugs in polymeric matrixes, the drug/CD nano- and microparticles are unstable and dissociate instantly upon media dilution, heating or addition of organic solvent to the aqueous complexation media. Thus, in aqueous solutions CDs behave more like organic solvents (e.g., ethanol) than disperse systems (e.g., nanosuspensions). Still, drug/CD complex nano- and microparticles possess many of the favorable properties of nanoparticulated drug delivery systems, such as enhanced drug delivery through biological membranes. Mucous membranes (mucosae) are epithelial layers that form a protective layer on, for example, the surface of the eye, nose and throat. Mucous membranes are covered by a gel-like fluid (called mucus) containing mainly water (~95%) and small amounts of mucins, proteins, lipids, polysaccharides and inorganic salts. Drug/CD complexes nano- and microparticles enhance drug delivery through mucous membranes by increasing drug permeation through the mucus layer without decreasing the ability of the lipophilic drug molecules to partition into and then permeate the lipophilic epithelial layers. Here self-assemble of CDs and drug/CD complexes to form nano- and microparticles will be discussed, determination of their critical aggregation concentration and how their unique physiochemical properties can be applied to enhance topical drug delivery to the eye. Only about 0.1 to 4% of a drug that is administered to the eye surface permeates into the anterior segment of the eye and drug delivery to the posterior eye tissue (e.g., to the retina) can only be achieved by injection. Here preparation and testing of fast dissolving aqueous eye drop microsuspension that can deliver therapeutic drug concentrations to the retina will be described. Finally, results of a phase II study of aqueous dexamethasone eye drops in diabetic macular edema will be shown.

Formation and charaterization of transient dryg/cyclodextrin complex nanoparticles and microparticles for drug delivery

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