Gastrointestinal tract drug delivery

Polymeric microparticles have been studied and developed for several years. Their contribution in the pharmacy field is of utmost importance in order to improve the efficiency of oral delivery of drugs. As drug carriers, polymer-based microparticles may avoid the early degradation of active molecules in undesirable sites of the gastrointestinal tract, mask unpleasant taste of drugs, reduce doses and side effects and improve bioavailability. Also, they allow the production of site-specific drug targeting, which consists of a suitable approach for the delivery of active molecules into desired tissues or cells in order to increase their efficiency. 

A number of the water-soluble polymers also have adhesive properties which are being extensively evaluated for drug delivery (9). These polymers will adhere to the mucous coating in the gastrointestinal tract, the nose, and the mouth to delay passage and sustain drug release. Those polymers with the best adhesive properties are those with hydroxyl and carboxyl groups. Table II lists some of the bioadhesive polymers and their adhesive properties. 

Delivery of either a small or large dose of the drug at the same rate Delivery of drug at the intended site of absorption irrespective of the region of the gastrointestinal tract where that process occurs... 

In the gastrointestinal tract, a mucoadhesive drug delivery system provides advantages in prolonging the residence time of devices. The use of pH-sensitive bioadhesive polymers has been proposed [26], An extensive review of pH-sensi-tive hydrogels is given by Brpndsted and Kopecek [27],... 

PK Gupta, S-H Leung, JR Robinson. Bioadhesive/mucoadhesives in drug delivery to the gastrointestinal tract. In V Lenaerts, R Gurny, eds. Bioadhesive Drug Delivery Systems. Boca Raton, FL CRC Press, 1990, pp 65-92. 

This model consists of a total of five compartments, the drug delivery system (DDS), the gastrointestinal tract (GIT), the central compartment (Central), and two elimination compartments denoted with a dashed box outline, one for pre-systemic elimination (Unavailable) and one for... 

Rouge N, Buri P, Doelker E (1996) Drug absorption sites in the gastrointestinal tract and dosage forms for site-specific delivery. Int J Pharm 136 117-139... 

The direct transport of absorbed drugs into systemic circulation, effectively by-passing the first-pass effect of the liver and gastrointestinal tract Lower enzymatic activity compared to the gastrointestinal tract or liver Amenability to self-medication, which increases patient compliance Possibility of pulsatile delivery of some drugs to simulate the biorhythmic release of these drugs Lower risk of overdosage Achievement of controlled release... 

A second example is the colon-specific delivery of glucocorticoids linked to dextran via a succinic acid or glutaric acid spacer [256a]. Such conjugates resist hydrolysis in the upper gastrointestinal tract, but are rapidly degraded by bacteria in the colon and caecum where little drug absorption occurs. 

The problems with this approach is that the intestinal pH may not be stable, since it is affected by diet, disease, and presence of fatty acids, carbon dioxide, and other fermentation products. Moreover, there is considerable difference in inter- and intraindividual gastrointestinal tract pH, which causes a major problem in reprodueible drug delivery to the large intestine [58]. 

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