Pseudolatex dispersions

Fig. 26 Differences observed in the mechanism of film formation from latex and pseudolatex dispersions and from micronized coating materials.

Aquacoat ECD and Surelease are two commercially available ethylcellulose pseudolatex dispersions. Aquacoat ECD. a product of FMC Corporation, is produced by an emulsification/solvent evaporation proce.ss that utilizes sodium lauryl sulfate and cetyl alcohol as colloid. stabilizers (64). The Aquacoat ECD dispersion contains approximately 27% ethylcellulose and 30% total solids. The dispersion does not contain plasticizer, and therefore an appropriate plasticizer must be added to the dispersion prior to coating. The dispersion is typically diluted to a final solids content in the range of 15-20% prior to spray coating. Although, intended to be a pH-independent sustained release coating system, the content of sodium lauryl sulfate in the Aquacoat ECD dispersion has been demonstrated to cause reduced drug release rates in acidic media versus media of neutral pH (65.66). 

Surelease. a product of Colorcon. is produced by first melt extruding ethylcellulose with oleic acid and dibutyl sebacate (DBS) (or fractionated coconut oil) to form a molten plasticized polymeric blend. This molten blend of plasticized ethylcellulose is then introduced into an ammoniated water solution under high shear and pressure to disperse small droplets of plasticized ethylcellulose into the water phase (67). Ammonium oleate is produced in situ during this emulsification process to stabilize the colloidal ethylcellulose particles (67). Additional purified water is then added to reduce the final solids content of the pseudolatex dispersion to 25%. The Surelease coating system does not contain an ionic surfactant, and therefore does not exhibit the pH-dependent drug relea.se observed with Aquacoat ECD (66),... 

EC is soluble in many organic solvents and insoluble in water, so the polymer can be applied to the substrate from (1) an organic solution, typically using a low MW alcohol, acetone, or a mixture thereof or (2) an aqueous pseudolatex dispersion. The term pseudolatex is used because the dispersed nanoparticles in an aqueous latex are considered to be produced from a polymerization reaction. Aqueous EC pseudolatexes, however, are produced utilizing either melt-processing... 

Another example of aqueous dispersions, known as pseudolatex dispersions, are readily available for use [77]. These are prepared by emulsion polymerization. However, the major pitfall surrounding these particles is that their preparation method still involves the use of organic solvents. 

Brian C, Li Jian-Xin. Pseudolatex dispersions for controlled drug delivery. In McGinity JW, Felton LA, editors. Aqueous polymeric coatings for pharmaceutical dosage forms, vol. 176 3rd ed. NY Informa Healthcare 2008. pp. 1-46. 

Another early attempt to formulate a nanoparticulate system for the delivery of pilocarpine was made by Gurny [99], This formulation was based on pilocarpine dispersed in a hydrogen CAP pseudolatex formulation. Gurny and co-workers [101] compared the formed nanoparticles to a 0.125% solution of hyaluronic acid some years after their first investigation and found that the viscous hyaluronic acid system showed a significantly longer retention time in front of the eye than the pseudolatex formulation. 

Examples of aqueous coating solutions include water-soluble low molecular weight cellulose ethers, emulsion polymerization latexes of polymethacrylates, and dispersions of water-insoluble polymers such as ethyl-cellulose in the form of pseudolatex. These solvent-free coating solutions provide a range of different coatings... 

The movement of the pharmaceutical industry away from volatile solvents for coating applications coupled with advancements in coating equipment design led to an increase in the popularity of latex and pseudolatex coating systems. Latexes and pseudolatexes are both colloidal dispersions of polymer droplets in a continuous aqueous phase, the difference between them being that latex systems are formed by emulsion polymerization... 

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