Absorption of drugs from the gastrointestinal tract
ABSORPTION OF DRUGS FROM THE GASTROINTESTINAL TRACT
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Before a drug can be absorbed, it must dissolve in the aqueous contents of the gut. Thus, the actual amount of the drug present in a dose is only one of the factors that will affect the amount of drug actually absorbed or available.
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Molecular size of the drug and its concentration
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Degree of ionizationĀ (depends on the pKa of the drug and pH of the medium)
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Lipid solubility of the neutral or nonionized form of the drug.
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Chemical or physical interaction with co-administered preparations and food constituents
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Pharmaceutical preparation and dosage form, especially their disintegration rate and dissolution rateĀ
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Gastric motility and secretion as well as gastric emptying
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Intestinal motility and secretion as well as intestinal transit time
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Fluid volume within the gastrointestinal tract
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Osmolality of the intestinal contents
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Intestinal blood and lymph flow
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Disruption of the functional and structural integrity of the gastric and intestinal epithelium
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Drug biotransformation within the intestinal lumen by microflora or within the mucosa by host enzymes
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Volume and surface area of the absorbing surface. Stomach has a relatively small surface area compared to the duodenum. Hence absorption is more in the duodenum.
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Presence of food in the stomach. Normally in full stomach there is a delay in absorption because the drug gets diluted in the stomach contents.
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Last modified: Wednesday, 25 April 2012, 5:45 AM