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25 Cards in this Set
- Front
- Back
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absorption
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the movement of a drug from its site of administration into the blood
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What factors affect drug absorption?
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Rate of dissolution- before a drug can be absorbed, it must first dissolve so the rate of dissolution helps determine the rate of absorption
surface area- the larger the SA, the faster the absorption will be blood flow- drugs are absorbed most rapidly from sites where blood flow is high lipid solubility- highly-soluble drugs are absorbed more rapidly than drugs whose lipid solubility is low pH partitioning- absorption will be enhanced when the difference b/n the pH of plasma and the pH at the site of administration is such that drug molecules will have a greater tendency to be ionized in the plasma |
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pharmacokinetics
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the study of drug movement throughout the body
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What must a drug pass in order to pass through a cell?
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cytoplasmic membrane
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What are the three ways a drug can cross a cell membrane?
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passage through channels or pores, passage with the aid of a transport system, and direct penetration of the membrane itself
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Very few drugs cross membranes via channels or pores. Why is this?
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The channels in membranes are extremely small and are specific for certain molecules, which means only the smallest of compounds (sodium or potassium) can pass through these channels.
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What are transport systems and why are they important?
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They are carriers that can move drugs from one side of the cell membrane to the other. All transport systems are selective. They are important b/c certain orally administered drugs could not be absorbed unless there were transport systems to movem them across the membranes that separate the lumen of the intestine from the blood. A number of drugs could not reach intracellular sites of action without a transport system to move them across the membrane.
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What are P-Glycoproteins and why are they important?
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They are transmembrane proteins that transport a wide variety of drugs OUT of cells. They are present in the liver (transporting drugs into the bile for elimination), kidney (transporting drugs into urine for excretion), placenta (back into the maternal blood), intestine (back into the intestinal lumen reducing drug absorption into the blood), and the brain capillaries (pumping drugs into the blood, limiting drug access to the brain)
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Why is movement of most drugs throughout the body dependent on the ability to penetrate membranes directly
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1. most drugs are too large to pass through channels or pores 2. most drugs lack transport systems to help them cross all of the membranes that separate them from their sites of action, metabolism, and excretion
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If a drug is to penetrate a membrane, what must it be?
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lipid soluble
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What groups are not lipid soluble and thus not able to directly cross membranes?
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polar molecules and ions (water)
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What are the common routes of administration?
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Enteral (via the GI tract)and Parenteral (IV, subQ, IM)
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Intravenous (barriers to absorption and absorption pattern)
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There are no barriers to absorption, IV administration results in "absorption" that is both instantaneous and complete
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What are the advantages of the intravenous route of administration?
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rapid onset, we have precise control over levels of drug in the blood, the ability to use a large volume of fluid (some drugs taht require parenteral admiistration are poorly soluble in water, and hence must be dissolved in a large volume), and last the use of irritant drugs is best done through IV (anticancer drugs are very chemically reactive and when administered through a freely flowing IV line can be rapidly diluted in the blood, thereby minimizing the risk of injury)
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What are the disadvantages of the IV route of administration?
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high cost, patients can't self-administer IV drugs due to the difficult technique, inconvenience due to the fact that patients are tethered to lines and bottles, irreversibility (if the dose is excessive, avoiding harm may be imposible), fluid overload (can be sig. prob. for patients with hypertension, kidney disease, or heart failure), infection (can occur from injecting a contaminated drug), embolism (insertion of IV needle can injure the venous wall, leading to formation of a thrombus, imbolism could result)
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Intramuscular (barriers to absorption and absorption pattern)
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barrier to absorption- the only barrier to absorption is the capillary wall, in capillary beds that serve muscles and most other tissues, there are "large" spaces b/n the cells that compose the capllary wall-drugs can pass through these spaces with ease
absorption pattern- rate of absorption is determined by water solubility of the drug and blood flow to the site of injection |
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What are the advantages of the IM route?
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This route is good for administration of poorly water soluble drugs. Also, the IM route can be used to administer depot preparations from which the drug is absorbed slowly over an extended time
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What are the disadvantages of the IM route?
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The two major disadvantages are discomfort and inconvenience. Also, if IM injections are done improperly, local tissue injury and possibly nerve damage can occur
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Oral route (barriers to absorption and absorption pattern)
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barriers to absorption- following oral administration, drugs may be asorbed from the stomach or intestine. In either case there are 2 barriers to cross 1. the layer of epithelial cells that lines the GI tract and 2. the capillary wall
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Describe the movement following absorption
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Drugs absorbed from all sites along the GI tract must pass through the liver before they can reach the general circulation. They go through the liver, enter the inferior vena cava, and eventually reach the general circulation.
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If a drug does not enter the general circulation what happens to it?
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Some drugs undergo extensive hepatic metabolism and others undergo secretion into the bile, after which they re-enter the small intestine (via the bile duct, and then either 1. undergo reabsorption into the portal blood, creating a cyle known as ENTEROHEPATIC RECIRCULATION or 2. exit the body in the stool
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What are the advantages of the oral route?
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it is easy, convenient, and inexpensive
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What are the disadvantages of the oral route?
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variability (a drug administered to one patient may be absorbed rapidly and completely, whereas the same drug given to another patient may be absorbed slowly and incompletely), inactivation (some drugs can't be taken orally b/c the acid in the stomach would destroy them), patient requirements (requires a conscious, cooperative patient), local irritation (can result in discomfort, nausea, and vomiting)
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distribution
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the movement of drugs throughout the body
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What three major factors determines drug distribution?
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1. blood flow to tissues 2. the ability of a drug to exit the vascular system 3. the ability of a drug to enter cells
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