国生 Ion-Exchange Systems Resint-drug +X-resint-X drug Ion-Exchange mechanism ·Resin-drug*+Y+→resin-Y++drug Ion exchange resins can form ionic complexes with oppositely charged drugs. The interactions between resin and drugs are strongly governed by the pH of the medium or by the presence of competing ions. The resin may release the drug in a certain region of the GIT,due to a pH change or presence of competing ions. 国生一 国丛生 Characteristics of ion-exchange Devices Other common oral time-controlled release ·Advantages systems Offers a protective mechanism for drugs ·Enteric release that are highly susceptible to degradation by enzymatic processes. ·Colonic release ·Disadvantages ·Pulsatile release .The release rate is proportional to the concentration of the ions present in the ·Bimodal release area of administration. 国生一 国秋生 Other common oral time-controlled release systems Other common oral time-controlled release systems ·Enteric release ·Enteric release Enteric release is intended to delay the release Drugs which have an irritant effect on the of the drug (or drugs)until the dosage form stomach,can be coated with an enteric film has passed through the stomach. that will only dissolve in the small intestine. Materials used for enteric coating prevent drug Enteric coating is also used to prevent the release in the stomach,because they are acidic environment of the stomach from typically acidic polymers that are stable degrading certain acid-labile medications. /insoluble at acidic pH. 66 Shanghai Jiao Tong University Ion-Exchange mechanism • Ion exchange resins can form ionic complexes with oppositely charged drugs. • The interactions between resin and drugs are strongly governed by the pH of the medium or by the presence of competing ions.. • The resin may release the drug in a certain region of the GIT, due to a pH change or presence of competing ions. Ion-Exchange Systems • Resin+-drug- + X- → resin+-X- + drug- • Resin- -drug+ + Y+→ resin- -Y+ + drug+ Shanghai Jiao Tong University Characteristics of ion-exchange Devices • Advantages • Offers a protective mechanism for drugs that are highly susceptible to degradation by enzymatic processes. • Disadvantages • The release rate is proportional to the concentration of the ions present in the area of administration. Shanghai Jiao Tong University Other common oral time-controlled release systems • Enteric release • Colonic release • Pulsatile release • Bimodal release Shanghai Jiao Tong University Other common oral time-controlled release systems • Enteric release • Enteric release is intended to delay the release of the drug (or drugs) until the dosage form has passed through the stomach. • Materials used for enteric coating prevent drug release in the stomach, because they are typically acidic polymers that are stable /insoluble at acidic pH. Shanghai Jiao Tong University Other common oral time-controlled release systems • Enteric release • Drugs which have an irritant effect on the stomach, can be coated with an enteric film that will only dissolve in the small intestine. • Enteric coating is also used to prevent the acidic environment of the stomach from degrading certain acid-labile medications