Drug Delivery Systems
- PDF / 880,967 Bytes
- 3 Pages / 604.8 x 806.4 pts Page_size
- 28 Downloads / 263 Views
ETIN/SEPTEMBER1991
treatment of hyperurecemia and goût; asparaginase for treatment of leukemia; and adenosine deaminase for treatment of a severe combined immunodeficiency. Microparticulates Microparticulates can be composed of proteins, lipids (for example, liposomes), carbohydrates, or synthetic polymers. Like drug-macromolecule conjugates, they may also alter bodily distribution of the drug, but they contain a greater amount of drug per unit volume. Liposomes hâve been the most widely studied of thèse microparticulates. They hâve been used to deliver such drugs as doxorubicin or amphotericin B for certain patients with cancer. Liposomes appear to be nontoxic, degradable, and nonimmunogenic. However, many liposomes exhibit poor stability during storage and use. Liposome stability may be improved by methods such as increasing liposomal cholestérol content or synthesizing polymerizable liposomes, but biodegradability may then be diminished. Engineering issues such as large-scale lipid production and manufacruring of liposomes are also critical to the more widespread use of thèse vesicles. In addition to liposomes, vesicles that contain magnetic particles hâve also been used to target drugs to spécifie locations in animal models via external magnetic fields. Controlled Release Systems Controlled release Systems deliver a drug at a spécifie rate for a definite time period. Release rates are generally determined by System design and are essentially independent of environmental conditions (e.g., pH). Thèse Systems can also deliver drugs for days or even years. Controlled release Systems differ from conventional "sustained" or "slow release" Systems that include complexes (to salts or ion exchange resins), suspensions, emulsions, slowly dissolving coatings that do not dissolve in the stomach yet do dissolve in the intestine (enteric coatings), and compressed tablets. Sustained release Systems generally émit drugs
in less than a day and environmental conditions do influence release rates, which leads to patient to patient variations. Controlled release Systems provide the following advantages over conventional drug thérapies: (1) maintenance of the drug in the desired therapeutic range by a single administration; (2) localizing delivery of the drug to a particular body compartment, lowering the total body drug level; (3) preserving drugs that are rapidly destroyed by the body (e.g., proteins); (4) reducing the need for follow-up care; (5) increasing comfort; and (6) improving compliance. Controlled release Systems are composed of either polymers or pumps. Pumps are larger and more expensive than polymeric Systems and require surgery for implantation; however, they enable very précise drug control and can release the drug directly into the bloodstream. Some pumps are also refillable. Both externally worn and implantable pumps are being used. In both cases, the driving force is a pressure différence, which results in bulk f low of a drug solution through an orifice. Polymeric materials generally release drugs by the follow
Data Loading...
