Stomach, release/stability

Some extended-release preparations are designed with a coating that responds to the acidity of its environment. The polymeric coating of the medicine is formulated for stability during oral delivery and for eventual solubility at the intended organ. The contrasting acidic content of the stomach and the more basic environment of the intestines enable these formulations to function. For example, hydroxypropyl methylcellulose phthalate (HPMCP) (Fig. 14.1.3) is an enteric... 

Usually salt formation is carried out to increase the solubility of the base, however, salts with lower solubilities are sometimes prepared to, e.g., mask taste, provide slower dissolution and increase chemical stability. An example of salt formation to decrease dissolution rate is described by Benjamin and Lin (1985), who prepared a range of salts of an experimental antihypertensive as shown in Table 3.10. The solubilities and intrinsic dissolution rates (IDR) of the prepared salts of this compound are also shown in Table 3.10. These in vitro tests showed that there were significant differences in the dissolution rate when the experiments were performed in water and buffer. However, the difference in the IDRs of the salts was similar in 0.1 M HC1. Hence, it was recommended that ebonate, 3-hydroxynaphthoate or napsylate salts should be formulated as enteric-coated dosage forms. This would avoid dissolution in the stomach acid, which could cause local GI irritation, and would still provide release of the compound. 

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