Drug release from tablets containing cellulose acetate phthalate as an additive or enteric-coating material

A formulation containing cellulose acetate phthalate for preparing enteric-coated granules was developed with the use of granulation and microencapsulation techniques. Drug release from tablets or tableted microcapsules was measured in a disintegration apparatus and an in vitro variable-pH release simulator of the flow type. The release mechanism for the tablets or tableted microcapsules was determined with the Higuchi matrix model, a first-order kinetic model, and the Weibull distribution function. Adding acetone directly to the mixture of sulfamethoxazole and cellulose acetate phthalate resulted in enteric-coated granules with more prolonged release than other granulation methods. Microencapsulation of the granules significantly delayed the drug release and enhanced the effectiveness of the enteric coating. Microencapsulated granules show release patterns that are sustained and can be simulated with three different release models, i.e., with square-root time plotting, diffusional first-order plotting, and Weibull distribution plotting. The enteric-coating behavior of the tablets was more clearly demonstrated with the variable-pH release stimulator than with a fixed-pH dissolution method.