Design and evaluation of water based pseudolatex enteric coating systems
Abstract
Disadvantages associated with solvent-based film coatings have led to renewed interest in the development of water based coating systems. This study was undertaken to develop totally aqueous coating systems, which are enteric, easy to be prepared and applied, and utilize FDA approved materials. Different approaches were attempted at the beginning of the project to investigate the feasibility of developing totally aqueous enteric coating systems. Among these approaches the annealing of an ethylcellulose pseudolatex, Aquacoat, with alkaline solutions of CAP was observed to produce coatings with excellent initial enteric properties. The project then focused on refining the CAP/Aquacoat systems, using a half factorial composite design, to produce commercially feasible coating systems. It was observed that at a high ethylcellulose content the coatings, on aging, failed to disintegrate in intestinal fluid, as a result of ethylcellulose coalescence. At a high CAP content, the coatings had poor gastric resistance, as a result of an increased gastric permeation of the coatings. The CAP/Aquacoat systems were enteric when applied to an erythromycin tablet core or to placebo tablets, but the application of the same systems to a sodium salicylate core tablet was observed to be non-enteric. This later effect was attributed to dissolution, at the core/coating interface, of sodium salicylate tablets by gastric fluid, which penetrated into the cores during gastric treatment. The dissolved sodium salicylate, due to its alkalinity, dissolved the CAP in the coatings, which led to the incomplete gastric resistance as observed. The free films of CAP salt produced from CAP solutions in alkaline solutions was observed to de-esterify, in the presence of excess alkali, to free phthalic acid. The free films of CAP produced from solution of CAP in ammonium bicarbonate solution developed a yellowish discoloration on aging. It was also found that these films degraded faster to free phthalic acid than films produced from CAP solutions in sodium or potassium hydroxide solutions. In this project the properties of individual component of the CAP/Aquacoat systems were also investigated, such as the x-ray and IR properties of CAP salt films, and the volatility of free films of the CAP/Aquacoat and plasticized Aquacoat systems.
Degree
Ph.D.
Advisors
Peck, Purdue University.
Subject Area
Pharmaceuticals
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