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17 Cards in this Set
- Front
- Back
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What 2 factors must be considered when you think about drug distribution?
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1. Distribution of cardiac output
2. rate of uptake by tissues |
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What is volume of distribution?
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Vd is an index of how extensively a drug is distributed to the body tissues compared to the plasma
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A higher Vd indicates what?
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More extensive distribution...meaning a low plasma concentration...meaning the drug is highly lipid soluble
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How do Vd values compare in the case of lipid soluble and lipid insoluble drugs?
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Lipid soluble drugs will have a higher Vd than that of lipid insoluble drugs.
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How does plasma protein binding affect plasma concentration and Vd values?
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If a large % of drug is bound to plasma proteins, the plasma concentraiton of the drug will be high and the Vd will be low.
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How does tissue binding affect plasma concentration and Vd values?
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If a large % of drug is bound to tissues, the plasma conc will be low, and the Vd will be high.
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Which tends to bind more to plasma proteins: acidic or basic drugs? Which tends to bind more to tissues?
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Acidic drugs tend to bind more to plasma proteins and basic drugs tend to bind more to tissues.
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So what if a drug binds more heavily to plasma proteins than to tissues...Why is that important?
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1. Drug + plasma proteins = decrease in drug action intensity
2. Drug + plasma proteins = less free drug is available for elimination 3. Drug + albumin is non-selective = drugs can compete with each other & with endogenous substances |
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Can the bound fraction of a drug diffuse thru membranes? What is the consequence?
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bound fraction of drug cannot pass thru membranes so it cannot be eliminated; EXCEPTION: a drug bound to plasma proteins does not prevent tubular active secretion of the drug
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What are the 5 examples of drug reservoirs within the body?
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1. plasma proteins
2. cellular reservoirs 3. fat 4. bone 5. transcellular reservoirs |
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Describe redistribution.
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Consider an anesthetic drug: initially the drug is in the blood and this blood goes to "vessel rich" organs; principally the brain. After a few minutes the drug starts to venture off into other tissues (fat, muscle etc). As it redistributes, the concentration in the brain decreases and the patient wakes up!
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What is the possible clinical consequence of warfarin displacement by a displacing drug?
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Excessive hypo-prothrombinemia and hemorrhage.
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What is the possible clinical consequence of tolbutamide displacement by a displacing drug?
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Hypoglycemia
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What is the significance of drug reservoirs in teh body?
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if a stored drug is in equilibrium with that in the plasma and is released as the plasma concentration declines, a drug concentration (1) in the plasma and (2) at its site of action can be sustained. in addition, pharmacological effects are prolonged.
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You measure the plasma concentration of a drug in your patient.
How do you calculate the Vd? |
Vd = (amt of drug in the body) / (conc of drug in plasma)
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This drug competes with bilirubin for binding to plasma albumin. This competition is especially dangerous in babies.
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Sulfonamides
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Why is it dangerous to give phenylbutazone to patients taking warfarin?
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Phenylbutazone and warfarin both bind to albumin. However, phenylbutazone has a higher affinity for albumin.
Phenylbutazone kicks warfarin off the albumin, which causes an increased free plasma concentration of warfarin. This leads to much greater anticoagulant effect. |
