Gastrointestinal route

Noninvasive drug delivery may require the administration of the drug delivery system (DDS) at an epithelium as a suitable site of absorption of the active compormd. Such regions are usually called mucosae. In the human body several mucosal sites can be identified, the one mostly used for administration and absorption of therapeutics being the gastrointestinal route. In order to increase the residence time at these absorption sites, a so-called mucoadhesive delivery system has to be used. Generally, these systems consist of one or more types of hydrogels. 

Specific type of mucoadhesive compounds, like lectins, have been evaluated to solve the difficulties presented by conventional mucoadhesive hydrogel systems, for instance in the gastrointestinal route. Since these compoimds do not belong to the class of hydrogels, they are not extensively discussed here. 

The buccal cavity is a useful alternative to the intestinal route for drag absorption in situations where the gastrointestinal route is unfeasible. Examples include ... 

RIFAMYCINS ANTIMALARIALS -ATOVAQUONE Both rifampicin and rifabutin L atovaquone levels, although the effect is greater with rifampicin (1AUC 50% cf. with 34% rifabutin) Uncertain because atovaquone is predominantly excreted unchanged via the gastrointestinal route Avoid co-administration with rifampicin. Take care with rifabutin and watch for poor response to atovaquone... 

Infection can occur through breaks in skin, by inhalation or gastrointestinal routes... 

Higher bioavailabiUty of the drugs than in the case of gastrointestinal route or pulmonary route... 

Vanadium is mainly absorbed via the respiratory and gastrointestinal routes. The oxidation state of vanadium does not appear to influence absorption (Carson et al.. 1986). In occupational exposure the main route of absorption is by inhalation of dust and fumes containing vanadium or vanadium compounds. 

Anthrax, a zoonotic disease caused by Bacillus anthracis, occurs in domesticated and wild animals—primarily herbivores, including goats, sheep, cattle, horses, and swine. Humans usually become infected by contact with infected animals or contaminated animal products. Infection occurs most commonly via the cutaneous route and only very rarely via the respiratory or gastrointestinal routes. 

Systemic delivery of drugs through the mouth has gained popularity in recent years. Drugs that are susceptible to degradation by the harshness of the gastrointestinal route can be administered via the mouth. This avoids first-pass metabolism of susceptible compounds by the hepatic system and offers the patient a more desirable route of administration than injection. Due to the limited area of the oral cavity, the delivery system itself is restricted in size, and hence potent compounds, such as proteins and peptides, are often more suited to such delivery systems. 

The oral route is undoubtedly the most widely investigated alternative administration route however, it presents major concerns in the delivery of macromolecular actives. The gastrointestinal route can promote degradation in the stomach due to the acidic gastric pH. The intestine has issues arising from the presence of proteolytic enzymes and insufficient permeation toward these actives, all of which result in limited bioavailability. Therefore, other routes of delivery have been investigated and the oral mucosal route presents a convenient alternative. 

Cholesterol molecules once formed in the body or absorbed from the diet can be eliminated from the human organism primarily by the gastrointestinal route as such or after conversion to bile acids. The latter are synthesized exclusively in the liver via a series of reactions which are initiated by 7a-hydroxylation of cholesterol (1). Bile acids subsequently formed are called primary bile acids, in contrast to secondary bile acids, which are formed by intestinal microorganisms from the primary ones during the enterohepatic circulation. 

Vanadium can be absorbed through the respiratory and gastrointestinal tracts, although the gastrointestinal route is the most studied. Vanadium occurs in the diet, or as a pharmacological agent, mainly as vanadyl or vanadate. Vanadate is transformed into vanadyl in the stomach [67], which primarily is the absorbed form. Most studies indicate that relatively little (<5%) ingested vanadium is absorbed and the remainder is excreted in the feces [68-74]. However, as with all substances, other dietary components probably affect absorption. The main route of excretion of absorbed vanadium is in the urine with lesser amounts lost in the feces, probably via the bile [74-77]. 

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