Physical Aging of Polymers and Its Effect on the Stability of Solid Oral Dosage Forms
Film coating is an effective method to modify drug release from tablets and pellets. Aqueous-based coating technology has become more popular due to environmental and regulatory requirements that restrict the use of organic solvents in production. The formation of thin, transparent lms from aqueous-based latex or pseudolatex dispersions occurs with the simultaneous evaporation of water [1,2]. Figure 14.1 is an illustration of lm formation from such systems. During the coating process (Stage I), water evaporates from the lm-coated substrate at a constant rate. The latex particles begin to pack together and fuse to form a continuous lm. As the colloidal particles begin to fuse and coalesce, as seen in Stage II, the rate of water evaporation decreases. By Stage III, lm formation is considered complete; however, it is during Stage III that changes occur in the drug-release rate due to physical aging of the polymeric lm coating.