Based on your answer in question 7 will the drug be absorbed in the stomach? Explain
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Because the interior of cell membranes is made of non-polar molecular regions, drugs with acid-base properties are better absorbed by cells when their most abundant form is not electrically charged (not an ion). In which region of the body will phenobarbital be absorbed at the lowest rate? (stomach, duodenum, jejunum).
Adi S.
The way that drugs get absorbed by the digestive system is often a function of pH. The buccal mucosa in the mouth has a pH of 6.5-7.0 and is the first point at which drugs may be absorbed. The stomach has a pH of about 2. Molecules that are charged in this state can be absorbed into the blood at that point. The intestinal mucosa, on the other hand, is non-polar and molecules that are uncharged in the stomach get absorbed there. Blood has a pH of about 7.4. In order for a molecule to pass the nonpolar cell membranes that make up the blood-brain barrier, the drug must be in its uncharged form. Below is the structure for oxycodone, a very strong painkiller. The nitrogen atom becomes protonated under acidic conditions. Modify the structure of the product below to show the protonated form of oxycodone. b. The pKa of this molecule is about 8.5. In the mouth, is it mostly charged or uncharged? In the conditions of the stomach, is it mostly charged or uncharged? d. In blood, is it mostly charged or uncharged? e. Describe how oxycodone makes its way to the brain.
Molecules that are hydrophobic may be able to penetrate the cell membranes in the stomach and intestine and pass into the bloodstream. Conversely, molecules that are charged or hydrophilic are generally not rapidly absorbed through such membranes. Thus, one can predict whether pharmaceutical compounds taken orally will be quickly absorbed in the stomach (pH 1.0-2.0) or whether they must pass into the intestine (more basic pH values) before being absorbed. Ambucetamide is a drug with a pKa of 8.4 of the amino group. Determine how this will be ionized (i.e., is the HA or A form drawn?). Calculate the percent of ambucetamide that will be available for absorption in the upper intestine (pH=5.0) versus the percent that can be absorbed in the lower intestine (pH=8.0).
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