Poloxamer colloidal systems

Ophthalmic delivery For administration of water-insoluble drugs into the eye, colloidal systems are used. Surface active polymers, such as polyvinyl alcohol, poloxamer, and methylcellulose are often added as particle stabilizers and viscosity enhancers. Particle size in such colloidal systems should not exceed 5-10 pm in diameter. Emulsions, liposomes, and micro- and nanoparticles, all stabilized by surfactants, are used in topical ophthalmic drug delivery [56]. For instance, an ophthalmic preparation of cyclosporin A, Restasis , is an emulsion stabilized by polysorbate 80 and polymer carbomer 1342. 

Poloxamers and other polymeric materials such as albumin may coat the micro- or nano particle, alter their surface characteristics and reduce their phagocytosis and opsonization by the reticuloendothelial system following IV injection. Such surface modifications often result in prolongation in the circulation time of intravenously injected colloidal dispersions.Poloxamers also have been used to stabilize suspension such as NanoCrystal . ... 

In dispersions stabilized on the basis of phospholipids, an additional fraction of very unstable particles was detected in the cryo-preparation. These particles possibly have a spherical shape as particles with an onion-like structure were detected in the freeze-fracture preparations. Due to the layered structure of the smectic phase, a cylindrical particle shape should be energetically more favorable than a spherical one. This may also be the reason for the higher sensitivity of spherical particles towards the electron beam. In formulations with polymeric stabilizers (e.g. poloxamer, polyvinyl alcohol and Tween 80), such highly unstable particles have not been detected yet. Polymer-stabilized smectic nanoparticles possess a more round, paving-stone-like particle shape. In dependence on the stabilizer system, additional colloidal structures (e.g. vesicles and micelles) formed by the excess of emulsifiers could be detected as well (Fig. 10.11). 

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