Oral route absorption sites

Drug release and retention at the site of absorption are very important for the enhancement of the bioavailability, particularly when the absorption sites are localized to a certain area of the GI route. This control of the transition of the drug can be achieved using bioadhesive excipients. Chlorothiazide (CT), a diuretic and antihypertensive drug, was better orally absorbed when administered with mucoadhesive polymers [25], The absorption of CT is considered to be saturable and site-specific, because a low dose is better absorbed, and a decreased stomach emptying rate and slow GI transition rate are better for increased absorption. As chitosan is a mucoadhesive polymer, the absorption of CT is expected to be enhanced... 

Metabolic activity may also constitute a considerable biochemical barrier to drag absorption. As described above, extensive enzymatic degradation of labile drugs in the gastrointestinal tract can severely limit their oral bioavailability. Other routes (nasal, buccal, transdermal etc.) are currently undergoing intensive investigations as possible sites of drug entry, partly, indeed often primarily, because these routes have lower enzymatic activity than the oral route and can avoid first-pass effects. 

Absorption is the transfer of a drug from its site of administration to the blood stream. The rate and efficiency of absorption depend on the route of administration. For intravenous delivery, absorption is complete, that is, the total dose of drug reaches the systemic circulation. Drug delivery by other routes may result in only partial absorption and thus lower bioavailability. For example, the oral route requires that a drug dissolve in the gastrointestinal fluid and then penetrate the epithelial cells of the intestinal mucosa disease states or the presence of food may affect this process. 

Absorption, Distribution, Metabolism, and Excretion. Information is needed on the comparative absorption of uranium compounds by the oral route, along with an assessment of its clearance from the skeleton. Quantitative data on the bioavailability of uranium from contaminated soil by the oral and dermal routes are also necessary to assess the risk of uranium-contaminated soil at hazardous waste sites. 

Cmcial to the whole subject is the process of dmg absorption, and how the physical properties of dmgs and their formulation can influence the rate and extent (and sometimes site) of absorption. The oral route and the many alternative routes to achieving systemic levels of drugs are reviewed in a chapter which... 

When a conventional (immediate-release) dosage form of a drug is administered orally or by other than intravenous (for example, i.m. or s.c.) injection, the half-life based on the decline phase of the plasma concentration-time curve is an apparent, rather than the true, half-life of the drug. This is because absorption continues after the time (fmax) of the observed peak plasma concentration (Cmax). The apparent half-life varies not only with the route (and site) of administration but also with the formulation of the dosage form of the drug (Baggot Brown, 1998). 

Among the various routes for gene therapy, the oral route is yet again the most attractive due to the ease of administration and high patient compliance. Efficient oral gene therapy provides an unparalleled opportunity for sustained production of therapeutic protein locally at the disease site in the gastrointestinal (GI) tract or at a site where maximum systemic absorption can occur due to increased residence and low proteolytic activity. Sustained production of therapeutic proteins in the GI tract has... 

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