| Enteric coating has been widely used to improve the chemical stability of acid sensitive drugs, reduce gastric stimulation and achieve targeting drug release in the colon and other fields. Organic polymer solutions coating is a traditional coating technology. The polymer membrane with compact structure was formed by evaporation of organic solvent. But organic polymer solutions have disadvantages especially in pellets coating as the high viscosity. Otherwise organic solvents have the characteristics of toxicity, volatile, flammable, explosive, expensive and potential environmental pollution. The applications of organic polymer solutions have been limited as the above reasons. Aqueous polymer dispersions are complex systems, which have the advantages of low toxicity, low viscosity, and shorter coating time. Usually, limited by the dispersion between the polymer and plasticizers in aqueous medium, as a result, the films formed by aqueous polymer dispersions are not as compact as the films formed by organic polymer solutions, and then affect some properties of films, such as permeability.A novel aqueous dispersion enteric coating material was prepared. Enteric coating material was dissolved in organic solvent, then adding plasticizers and, if desired or required, further auxiliary agents. Eudragit(?)L100-55 aqueous dispersion was prepared after emulsification with water and evaporation removed the organic solvent. Free films of Eudragit(?)L100-55 aqueous dispersion, Eudragit(?)L100-55 organic solution and Eudragit(?)L30D-55 aqueous dispersion were prepared by casting method. Properties of the free films including appearance, glass transition temperature (Tg), permeability and solubility were investigated. Results displayed that when the content of triethyl citrate (TEC) was 5%, the permeability of Eudragit(?)L100-55 aqueous dispersion film was the similar to its organic film, and both of them were lower than that of Eudragit(?)L30D-55 aqueous dispersion film. When the content of TEC was 10%, the Tg values of the Eudragit(?)L30D-55 aqueous dispersion film, the Eudragit(?)L100-55 aqueous dispersion film and the Eudragit(?)L100-55 organic film were 58.17℃,53.63℃ and,51.70° respectively. When the content of TEC was enhanced 20%, the Tg values of the Eudragit(?)L30D-55 aqueous dispersion film, Eudragit(?)L100-55 aqueous dispersion film and the Eudragit(?)L100-55 organic film were 50.95℃,41.72℃ and, 32.25℃ respectively. The data size comparison of the Tg values of these three kinds of free film is as follow, Eudragit(?)L30D-55 aqueous dispersion film> Eudragit(?)L100-55 aqueous dispersion film>Eudragit(?)L100-55 organic film. Under the same content of plasticizer in prescription of enteric coating dispersion, Tg values, permeability and the solubility in 0.1mol/L HCl of Eudragit(?)L30D-55 aqueous dispersion film were lower than those of Eudragit(?)L30D-55 aqueous dispersion film.Pantoprazole sodium (PAZ-Na) was selected as a model drug to study properties of three enteric coating films. PAZ-Na containing pellet cores were prepared by extrusion spheronization method. PAZ-Na enteric pellets within an isolation lay with HPMC and enteric coating lay with Eudragit(?)L100-55 aqueous dispersion, Eudragit(?)L100-55 organic solution or Eudragit(?)L30D-55 aqueous dispersion respectively, were prepared by using by rotary fluidized-bed equipment. The acid resistance and release property of pellets were studied. During the process of coating, viscosity of Eudragit(?)L100-55 aqueous dispersion was lower than its organic solution, and the time of coating process could shorten, and just similar as the Eudragit(?)L30D-55 aqueous dispersion. When the coating increased weights was 9%, the residues of PAZ-Na after 2 h in 0.1mol/L HCl of the Eudragit(?)L30D-55 aqueous dispersion enteric coating pellets, the Eudragit(?)L100-55 aqueous dispersion enteric coating pellets and the Eudragit(?)L100-55 organic solution enteric coating pellets were 76.21%,86.44% and 85.19% respectively. Accordingly, the losses of PAZ-Na were 23.79%,13.56% and 14.81% respectively. When the coating increased weight was 12%, the residues of PAZ-Na after 2 h in O.lmol/L HCl of the Eudragit(?)L30D-55 aqueous dispersion enteric coating pellets, the Eudragit(?)L100-55 aqueous dispersion enteric coating pellets and the Eudragit(?)L100-55 organic solution enteric coating pellets were 88.87%,94.52% and 93.78% respectively. Accordingly, the losses of PAZ-Na were 11.13%,5.48% and 6.22% respectively. The results displayed that the acid resistances of Eudragit(?)L100-55 aqueous dispersion and Eudragit(?)L100-55 organic solution were better than that of Eudragit(?)L30D-55 aqueous dispersion, and the less increased coating weight and process time could reach to desired acid resistance.The results of this research show that the thermodynamic property, permeability, solubility and acid resistance of Eudragit(?)L100-55 aqueous dispersion which prepared by adding plasticizer by the method of emulsification and evaporation, were similar as its organic solution, and better than those of Eudragit(?)L30D-55 aqueous dispersion. Meanwhile, this method not only kept the advantages of quick and convenient of the conventional aqueous dispersion coating method but also possess more application prospect. |
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