Pharmacology Chapter on Drug Distribution
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Questions and Answers

What is a consequence of inhibiting drug metabolism over an extended period?

  • Shortened pharmacological effects
  • Increased drug-induced toxicities (correct)
  • Decreased plasma levels of the drug
  • Enhanced drug elimination

Which phase of drug metabolism involves the addition of hydroxyl groups?

  • Phase II reactions
  • Enzymatic degradation
  • Tubular reabsorption
  • Phase I reactions (correct)

Which of the following routes is NOT primarily associated with drug elimination by the body?

  • Bile
  • Skin (correct)
  • Kidney
  • Lung

How do Phase II metabolic reactions increase drug polarity?

<p>By conjugating with polar substances (C)</p> Signup and view all the answers

Which process is involved in the renal elimination of drugs?

<p>Glomerular filtration (A)</p> Signup and view all the answers

What primarily determines the rate at which a drug leaves the bloodstream to enter tissues?

<p>Blood flow (B)</p> Signup and view all the answers

Why does thiopental produce a short duration of action after intravenous administration?

<p>High blood flow to the CNS (D)</p> Signup and view all the answers

How does capillary permeability influence drug distribution?

<p>It allows drugs to cross into the tissue (B)</p> Signup and view all the answers

What characterizes capillaries in the blood-brain barrier?

<p>Continuous capillary structure (C)</p> Signup and view all the answers

Which factor is most likely to prevent a drug from entering the central nervous system?

<p>Low blood flow to the brain (D)</p> Signup and view all the answers

What should occur for a large neutral amino acid to be transported into the brain?

<p>Active transport via specific transporters (C)</p> Signup and view all the answers

What is the effect of high hydrophobicity on drug distribution?

<p>Facilitates entry into CNS (A)</p> Signup and view all the answers

Which of the following is NOT a factor influencing drug distribution?

<p>Concentration of the drug in the urine (B)</p> Signup and view all the answers

What primarily prevents ionized or polar drugs from entering the CNS?

<p>Endothelial cells of the CNS form tight junctions. (A)</p> Signup and view all the answers

How do hydrophobic drugs primarily cross biological membranes?

<p>Through passive diffusion in lipid membranes. (C)</p> Signup and view all the answers

What is the major drug-binding protein in plasma?

<p>Albumin. (A)</p> Signup and view all the answers

What effect does binding to plasma proteins have on drug activity?

<p>Bound drugs are pharmacologically inactive. (A)</p> Signup and view all the answers

What happens to the free-drug concentration when a bound drug dissociates from albumin?

<p>It remains constant as a fraction of total drug. (D)</p> Signup and view all the answers

What is a characteristic of hydrophilic drugs in relation to cell membranes?

<p>They require slit junctions to cross membranes. (A)</p> Signup and view all the answers

What occurs when two drugs compete for binding to plasma albumin?

<p>One drug may displace the other. (B)</p> Signup and view all the answers

What effect do drugs like phenobarbital and rifampin have on CYP isozymes?

<p>They induce the synthesis of CYP isozymes. (C)</p> Signup and view all the answers

What is the impact of hypoalbuminemia on drug levels in the plasma?

<p>It alters the level of free drug. (D)</p> Signup and view all the answers

Which of the following is a consequence of increased drug metabolism through CYP isozymes?

<p>Decreased therapeutic drug effect. (B)</p> Signup and view all the answers

What is a common mechanism by which drugs inhibit CYP isozyme activity?

<p>Competing for the same isozyme. (A)</p> Signup and view all the answers

Which drug is a potent inhibitor of multiple CYP isozymes responsible for warfarin metabolism?

<p>Omeprazole (A)</p> Signup and view all the answers

Which substance can induce CYP1A2, affecting the metabolism of amitriptyline and warfarin?

<p>Polycyclic aromatic hydrocarbons (B)</p> Signup and view all the answers

What is a potential consequence of taking a CYP inhibitor like erythromycin with another medication?

<p>Enhanced adverse effects of the other medication. (D)</p> Signup and view all the answers

Which of the following is NOT a common CYP inhibitor?

<p>Ibuprofen (C)</p> Signup and view all the answers

What is the result of increased biotransformations of drugs via CYP isozymes?

<p>Variability in drug effectiveness depending on metabolite activity. (A)</p> Signup and view all the answers

What defines Class I drugs in relation to their binding to albumin?

<p>Their dose is less than the binding capacity of albumin. (A)</p> Signup and view all the answers

Which drug is considered a Class I drug under standard classifications?

<p>Warfarin (A)</p> Signup and view all the answers

What is a major consequence of administering a Class II drug to a patient already taking a Class I drug?

<p>Increased concentration of free Class I drug. (A)</p> Signup and view all the answers

How are lipophilic drugs typically transformed during metabolism?

<p>Into more polar products for easier excretion. (C)</p> Signup and view all the answers

Which organ is primarily responsible for drug metabolism?

<p>Liver (A)</p> Signup and view all the answers

What happens to warfarin when a sulfonamide is administered?

<p>The concentration of unbound warfarin rises. (B)</p> Signup and view all the answers

What does the term 'induction' refer to in the context of cytochrome P450 enzymes?

<p>Increased activity of specific CYP isozymes. (B)</p> Signup and view all the answers

Pro-drugs must undergo what process to become active?

<p>Biotransformation. (D)</p> Signup and view all the answers

Flashcards

Drug Distribution

The process by which a drug moves from the bloodstream into the tissues and cells. It's like the drug is being distributed to different parts of the body.

Blood Flow

The rate at which blood flows to different tissues. It's like a highway system where some roads carry more traffic than others.

Capillary Permeability

How easily a drug can pass through the walls of blood vessels into the tissues. It's like a fence with different sized holes.

Lipid Solubility

The ability of a drug to dissolve in fats. It's like a key fitting into a lock.

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Drug Binding to Proteins

The tendency of a drug to bind to proteins in the blood or tissues. It's like two magnets sticking together.

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Blood-Brain Barrier

The barrier that protects the brain from harmful substances. It's like a gatekeeper who controls what goes in and out.

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Large Neutral Amino Acid Transporter

A special transporter that helps levodopa enter the brain. It's like a shuttle taking passengers to their destination.

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Drug Redistribution

The process by which a drug moves from one area of the body to another, impacting the duration of its effect. It's like a drug taking a detour.

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Drug Metabolism

The process of converting drugs into more water-soluble forms, primarily in the liver. This helps the body eliminate drugs more efficiently.

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Phase I Reactions

These reactions involve adding hydroxyl groups or removing blocking groups from existing ones, making the drug more polar.

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Phase II Reactions

These reactions attach polar molecules like sulfate, glycine, or glucuronic acid to the drug, further increasing its water solubility.

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Drug Elimination

The process of eliminating a drug from the body, mainly through the kidneys into the urine.

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Distal Tubular Reabsorption

Refers to the reabsorption of drugs back into the bloodstream from the kidney tubules. This can lead to prolonged drug effects if the drug is not efficiently eliminated.

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CYP Isozyme Induction

Certain drugs like phenobarbital, rifampin, and carbamazepine can increase the production of specific CYP enzymes, leading to faster breakdown of other drugs.

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Decreased Plasma Drug Concentration

When a drug's metabolism is sped up, its concentration in the blood decreases, potentially reducing its effectiveness.

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CYP Isozyme Inhibition

Some drugs can block CYP enzymes, slowing down the metabolism of other drugs and increasing their concentration in the blood.

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Increased Plasma Drug Concentration

When a drug's metabolism is slowed down, its concentration in the blood increases, potentially leading to stronger effects or even toxicity.

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Competitive CYP Inhibition

A drug that is a substrate for a specific CYP enzyme may also inhibit the same enzyme, affecting other drugs metabolized by that enzyme.

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Non-Competitive CYP Inhibition

Some drugs can inhibit CYP enzymes even if they are not themselves broken down by those enzymes, potentially leading to interactions with other drugs.

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CYP Isozyme Interactions

CYP isozyme induction and inhibition can have significant impacts on how drugs interact with each other, potentially causing changes in drug effectiveness or increasing the risk of side effects.

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Broad CYP Inhibitors

Certain drugs like erythromycin, ketoconazole, and ritonavir can inhibit multiple CYP enzymes, leading to potential interactions with a wide range of other drugs.

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Class I Drugs

Drugs with a high affinity for albumin that are given in doses lower than the binding capacity of albumin. These drugs have a high bound-drug fraction, meaning most of the drug is attached to albumin and not free to exert its effects.

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Class II Drugs

Drugs with a high affinity for albumin that are given in doses exceeding the binding capacity of albumin. These drugs have a high free-drug fraction, meaning a large portion is not bound to albumin and is free to exert its effects.

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Drug Displacement

The process of one drug displacing another from its binding site on albumin, leading to an increase in the concentration of the displaced drug in its free form.

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Pro-drugs

Inactive compounds that must be metabolized into their active forms to exert their therapeutic effects.

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Liver

The main organ responsible for drug metabolism, converting lipophilic drugs into more polar and excretable metabolites.

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Cytochrome P450 (CYP) Isozymes

A family of enzymes that play a key role in drug metabolism. These enzymes are responsible for breaking down and eliminating many drugs from the body.

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CYP Induction

The process by which certain drugs increase the activity of specific CYP isozymes, leading to increased metabolism of other drugs.

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Blood-Brain Barrier and Drug Entry

Polar or ionized drugs, due to their charge, struggle to cross the blood-brain barrier, making them less effective in reaching the central nervous system. This barrier is formed by tightly packed cells in the CNS with no gaps, preventing these drugs from easily passing through.

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Hydrophobic Drug Movement

Hydrophobic drugs, with uniform electron distribution, readily cross cell membranes because they can dissolve in lipid membranes, the building materials of these membranes. This allows them to spread throughout the cell.

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Hydrophilic Drug Movement

Hydrophilic drugs, with uneven electron distribution or a charge, have difficulty crossing cell membranes. They need to use special pathways, like gaps between cells, to get through.

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Drug Binding to Plasma Proteins

Binding of drugs to plasma proteins, primarily albumin, can temporarily store drugs in the blood, making them less readily available to enter tissues. This reversible binding acts as a reservoir, releasing the drug when needed.

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Competition for Binding Sites

When two drugs compete for the same binding sites on albumin, they can interfere with each other's ability to bind and be stored in the blood. This competition can affect the amount of free drug available for action.

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Hypoalbuminemia and Free Drug Levels

Low albumin levels in the blood can lead to more free drug available for action, because less is bound to the protein. This can affect the drug's effects and potentially increase its toxicity.

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Bound vs. Free Drugs

Bound drugs are inactive, meaning they cannot interact with the target cells to produce an effect. Only free, unbound drugs can reach the target sites and exert their pharmacological actions.

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Free Drug Concentration

The amount of free drug in the blood is a constant fraction of the total drug in the plasma. This fraction represents the balance between drug binding and release, ensuring a consistent amount of active drug.

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Study Notes

Drug Distribution

  • Drug distribution is the reversible movement of a drug from the bloodstream into the interstitial fluid and/or cells of tissues.
  • Factors affecting drug delivery from plasma to interstitial fluid:
    • Blood flow to the tissue
    • Capillary permeability
    • Drug's hydrophobicity
    • Binding to plasma and tissue proteins

Blood Flow

  • Blood flow to tissues varies, influenced by the unequal distribution of cardiac output.
  • Higher blood flow to the brain, liver, and kidneys compared to skeletal muscle and adipose tissue.
  • Differences in blood flow influence the duration of drug effects, like the short duration of thiopental hypnosis.
  • High blood flow and high lipid solubility of thiopental allows rapid CNS entry and anesthesia induction.

Slower Distribution to Skeletal Muscle and Adipose Tissue

  • Slower distribution to skeletal muscle and adipose tissue decreases plasma concentration and returns consciousness.
  • Redistribution is a phenomenon with various compounds with similar properties.

Capillary Permeability

  • Capillary permeability is influenced by the structure and chemical nature of the drug.
  • Capillaries in the brain are continuous, lacking slit junctions, differing from the liver and spleen with their large, discontinuous capillaries and exposed basement membranes.
  • Lipid-soluble drugs readily permeate the CNS, while charged or polar drugs face barriers due to the tight junctions.

Blood-Brain Barrier

  • For drugs to enter the brain, they must pass through the CNS endothelial cells or be actively transported.
  • Lipid-soluble drugs readily cross, while ionized drugs or polar substances are impeded.
  • The specific transporter carries levodopa into the brain.
  • The blood-brain barrier is critical for protecting the brain from many substances.

Drug Structure

  • Hydrophobic drugs readily cross cell membranes due to a uniform electron distribution and lack of charge.
  • Hydrophilic drugs, with their uneven electron distribution and charge, must use slit junctions for passage.
  • High blood flow directly influences the distribution of hydrophobic drugs.

Binding of Drugs to Plasma Proteins

  • Reversible binding to plasma proteins sequesters drugs in an inactive form in the vascular compartment, slowing transfer.
  • Binding is non-selective regarding chemical structure.
  • Plasma albumin is the principal binder and acts as a reservoir.
  • If free drug concentration decreases, bound drug dissociates to maintain a relatively constant free-drug level.

Binding of Class I and Class II Drugs to Albumin

  • Class I drugs have a lower dose than binding sites, resulting in a low dose/capacity ratio with high bound-drug fraction. These are common in clinical use.
  • Class II drugs have a much higher dose than binding sites, resulting in a high dose/capacity ratio with a high free-drug fraction.

Competition for Binding Between Drugs

  • When two drugs with high affinity for albumin are administered, they compete for binding sites.
  • Drug dose relative to albumin binding capacity dictates the resultant free drug/bound drug ratio and subsequent pharmacological effect.

Drug Metabolism

  • Drugs are often eliminated through biotransformation or excretion in the urine or bile.
  • The liver primarily metabolizes lipophilic drugs into polar, excretable products.
  • Some drugs, known as pro-drugs, are initially inactive and must be metabolized into their active forms.
  • Biotransformation occurs in phases I and II, with phase I modifying drugs and phase II conjugating to increase polarity.

P450 Isozymes

  • P450 isozymes are a group of liver enzymes crucial for drug metabolism.

Drug Metabolism and Induction/Inhibition of P450

  • Certain drugs like phenobarbital, rifampin, and carbamazepine increase CYP isozyme synthesis increasing drug metabolism, which can lead to decreased drug levels.
  • Inhibitors of certain isozymes block drug metabolism, which can cause elevated plasma levels and increase risk of adverse drug effects.

Consequences of Increased Drug Metabolism

  • Increased drug metabolism can decrease drug activity if the metabolite is inactive.
  • Increased drug activity if the metabolite is active.
  • Decreased therapeutic effects.
  • Polycyclic aromatic hydrocarbons (air pollutants) can induce CYP1A. This affects drugs like amitriptyline and warfarin, decreasing their therapeutic concentration.

Drug Elimination

  • Drug removal from the body occurs via various routes, but primarily through the kidneys into the urine.
  • Other routes include the intestines, bile, and lungs.
  • Renal elimination involves glomerular filtration, proximal tubular secretion, and distal tubular reabsorption.

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Drug Distribution PDF

Description

This quiz explores the principles of drug distribution within the body, focusing on how various factors impact drug delivery from the bloodstream to tissues. Key topics include the effects of blood flow, capillary permeability, and the implications of drug hydrophobicity. Test your understanding of how these factors influence drug effects and duration.

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