Facts about deug absorption and its pharmacokinetics?
Answer:
Pharmacokinetics basically asks the question, "Is the drug getting to its site of action?"
It is usually considered under four headings (acronym: ADME):
Absorption (how much drug is available to the body and how fast)
Distribution (where the drug goes within the body)
Metabolism (how the drug is affected by the body)
Elimination (how the body gets rid of the drug)
The factors affecting the rate of absorption include:
* The formulation (e.g. some coatings of pills are harder to dissolve than others)
* GIT motility (most drugs are absorbed in the first part of the small intestine, so the longer it takes for the stomach to empty, the slower the drug gets absorbed)
* Malabsorptive states (in some forms of intestinal disease, e.g. coeliac disease, drugs can't be absorbed as well)
* Other food (e.g. milk reduces the absorption of some antibiotics)
One other thing to add is that we usually refer to a drug's "bioavailability" rather than it's absorption. Bioavailability is basically a measure of how much of the drug becomes available to the body to potentially affect its target site. It includes absorption, but it also takes into account any metabolism that takes place before the drug enters the systemic circulation. To illustrate this, consider a tablet that you swallow, in the hope that it relieves your joint pain.
Clearly, the tablet can only have an effect if it is absorbed from the gastrointestinal tract (GIT) into the blood stream. However, this is not enough by itself: the blood from the GIT passes through the liver and then the lungs before it is available to the rest of the body (via the systemic circulation). Thus, for a drug to work, not only must some of it be absorbed, but at least some of it must reach the site of action (e.g. your painful joints) without being metabolised by the GIT, liver, or lungs.
Now, if you take a blood level for your drug, all you have an idea of is how much of the drug is available to the body. It can be very hard to determine how much of the drug was lost through not being absorbed, versus how much of the drug was lost through pre-systemic metabolism. Therefore, we usually talk simply of "bioavailability" (how much of the drug is available to the systemic circulation) rather than absorption, since we don't know exactly how much WAS absorbed in the first place.
The short answer is that pharmacokinetics is the study of how drugs are Absorbed, Distributed, Metabolized and then Excreted from the body.
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