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What primarily determines the distribution of a drug within the body?
Which type of drugs can cross the blood-brain barrier (BBB)?
What effect does the binding of drugs to plasma proteins have on their action?
Which organ typically has the highest blood flow impacting drug distribution?
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What is the role of the placenta in drug distribution?
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In drug distribution, what type of drugs typically bind to albumin?
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Which of the following is TRUE about the distribution of warfarin and morphine?
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What is a consequence of having a drug that is 0% bound to proteins?
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Which class of drugs is characterized by a low dose/capacity ratio and a high bound-drug fraction?
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What is the clinical consequence of administering a class II drug to a patient taking a class I drug?
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What determines a drug's volume of distribution (Vd) when it is mostly retained in the plasma?
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Why are drugs with a large volume of distribution (Vd) like pithidine not easily removed by hemodialysis?
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Which of the following statements regarding binding of drugs to albumin is true?
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What is the role of free, unbound drugs in the body?
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How does hypoalbuminemia affect drug distribution?
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What percentage of body weight is total body water in an average 70-kg individual?
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Which factor primarily influences the half-life of a drug?
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What happens when a highly bound drug like warfarin is displaced from plasma proteins?
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What is the relationship between volume of distribution and drug availability to excretory organs?
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Which of the following statements about tissue binding is incorrect?
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What is the primary binding protein for drugs in plasma?
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Which type of drugs tend to have a large volume of distribution?
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How does drug structure influence pharmacokinetics?
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What is a significant clinical relevance of knowing a drug’s volume of distribution (Vd)?
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What is one effect of competition for plasma protein binding between two drugs?
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What is one consequence of chronic renal failure on drug binding?
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What effect does tissue accumulation of drugs have on elimination?
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In cases of drug poisoning, which type of drug is typically harder to remove via hemodialysis?
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If a drug is mostly retained in the plasma, what can be inferred about its volume of distribution?
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What is the primary characteristic of hydrophilic drugs that limits their ability to penetrate cell membranes?
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How is the volume of distribution (Vd) defined?
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What is the equation used to calculate the plasma concentration of a drug?
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If a drug has a molecular weight that is very high, what will most likely happen?
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What is true regarding the distribution of hydrophilic drugs?
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How is apparent volume of distribution (L/kg) calculated?
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In an example where a 500 mg dose of a drug results in a plasma concentration of 10 mg/L, what is the volume of distribution?
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Aminoglycoside antibiotics are known to have which type of drug distribution?
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Study Notes
Drug Distribution
- Drug distribution is the movement of a drug from the bloodstream into the interstitial fluid and/or tissues.
- Factors influencing drug distribution include blood flow, capillary permeability, protein binding, and tissue binding.
Blood Flow
- Blood flow varies between tissues, impacting drug distribution.
- Organs like the brain, liver, and kidney receive more blood flow than skeletal muscles.
- Adipose tissue has lower blood flow.
- High blood flow and lipid solubility allow drugs like thiopental to rapidly reach the central nervous system (CNS) for anesthesia.
Capillary Permeability
- Capillary structure varies depending on the junctions between endothelial cells.
- The blood-brain barrier (BBB) is formed by tight junctions between endothelial cells and surrounding glial cells.
- Only lipid-soluble, unionized drugs can cross the BBB.
- The placental barrier allows lipid-soluble, unionized drugs to pass through, potentially affecting the fetus.
Drug Binding
Plasma Protein Binding
- Most drugs in the bloodstream bind to plasma proteins, primarily albumin for acidic drugs and alpha-acid glycoprotein for basic drugs.
- Only the unbound fraction of a drug is pharmacologically active, while the bound fraction acts as a reservoir.
- Protein binding varies for each drug, influencing its duration of action.
- Hypoalbuminemia can alter the level of free drug.
Tissue Binding
- Drugs can accumulate in tissues, leading to higher concentrations compared to plasma.
- Tissue binding can prolong drug action or cause local toxicity.
- Examples include the accumulation of acrolein, a cyclophosphamide metabolite, in the kidney leading to renal toxicity.
Volume of Distribution (Vd)
- Vd is a hypothetical volume representing the distribution of a drug throughout body compartments.
- Vd is calculated by dividing the amount of drug in the body by the plasma concentration.
- Vd is influenced by drug properties and body composition.
- A large Vd implies that the drug is widely distributed in the body, potentially leading to a longer half-life.
Body Water Compartments
- Drugs distribute into different body water compartments based on their properties.
- Plasma compartment: Drugs with large molecular weight or high plasma protein binding remain confined to the plasma.
- Extracellular fluid: Hydrophilic drugs with low molecular weight distribute into the plasma and interstitial fluid.
- Total body water: Hydrophobic drugs with low molecular weight can distribute into plasma, interstitial fluid, and intracellular fluid.
Drug Displacement
- Drugs with high affinity for albumin can compete for binding sites.
- Displacement interactions can occur when two drugs compete for the same binding site, potentially altering the free drug concentration and therapeutic effects.
- For example, sulfonamide antibiotics can displace warfarin from albumin, increasing the free warfarin concentration and the risk of bleeding.
Clinical Significance of Vd
- Vd is important for calculating drug dosage and understanding drug elimination.
- Drugs with large Vd are harder to remove by hemodialysis due to their extensive distribution.
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Description
This quiz covers essential concepts of drug distribution, including factors such as blood flow, capillary permeability, and tissue binding. It explores how these elements impact the movement of drugs throughout the body and their accessibility to various organs. Mastering these concepts is crucial for understanding drug action and efficacy.
