Subject drug release systems

Use of locust bean as sustained release agent [54], carrier [54,65,66], disintegrant [54,67] and bioadhesive agent [66] has been the subject of research studies. Locust bean gum is promising for use in controlled drug release systems targeting the colon [54]. 

Hydrogels have received increasing interest for biomedical and consumer products application [98]. PLA and PEG hydrophilic/hydrophobic block copolymers are especially promising for soluble hydrophilic/hydrophobic system that becomes an insoluble microsphere when injected into the body as drug release systems [99]. The hydrolysis and biodegradation of these copolymers are subjects of ongoing research. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

Long-term controlled release of drugs from inert matrices has been subject of numerous scientific investigations (e.g. refs. [1-7]). The easily manufactured release systems may be applied as subcutaneous implants in humans and for veterinary use. They are helpful in many other areas too, for instance in agriculture [8]. 

Microencapsulation has been the subject of massive research efforts since its inception around 1950. Today, it is the mechanism utilized by approximately 65% of all sustained-release systems [35], The technique s popularity can be attributed mainly to its wide variety of applications. Hundreds of drugs have been microencapsulated and used as controlled-release systems. Some examples are Arthritis Bayer, Dexatrim Capsules, and Dimetapp Elixir. 

Among newly developed colon-specific drug delivery systems, pressure-controlled delivery capsules (PCDCs) [161] can be mentioned. Their mechanism of action is based on the relatively strong peristaltic waves taking place in the colon and leading to an increased luminal pressure. They consist of a capsular-shaped suppositories coated with a water-insoluble polymer (ethyl cellulose). Once taken orally, PCDCs behave like an ethyl cellulose balloon, because the suppository base liquefies at body temperature. In the upper GI tract, PCDCs are not directly subjected to the luminal pressures since sufficient fluid is present in the stomach and small intestine. The reabsorption of water in the colon provokes an increase of the luminal content viscosity. As a result, increased intestinal pressures directly affect the system via colonic peristalsis. Consequently, PCDCs mpture and drug release in the colon take place. 

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