Drug Metabolism
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Questions and Answers

What is the primary organ responsible for drug metabolism?

  • Liver (correct)
  • Lungs
  • Kidneys
  • Heart

    • Which of the following best defines drug metabolism?

  • The processes by which biochemical reactions alter drugs within the body (correct)
  • The absorption of drugs into the bloodstream
  • The process of drug synthesis in laboratories
  • The distribution of drugs throughout the body

    • What is a possible outcome of drug biotransformation?

  • Active drug being excreted unchanged
  • All drugs must be converted to hydrophilic compounds
  • Conversion of a toxic metabolite to an inactive metabolite
  • Formation of an active drug from an inactive prodrug (correct)

    • Which statement accurately describes the relationship between Phase I and Phase II reactions?

    <p>Phase I reactions generally introduce functional groups, while Phase II reactions typically conjugate metabolites.</p> Signup and view all the answers

    What type of drug may be converted into an active drug through biotransformation?

    <p>An inactive prodrug</p> Signup and view all the answers

    Why might lipophilic drugs pose challenges for renal excretion?

    <p>They are difficult to dissolve in aqueous urine.</p> Signup and view all the answers

    Which reaction is considered a Phase I biotransformation?

    <p>Hydroxylation of the drug molecule</p> Signup and view all the answers

    Which of the following is NOT a potential outcome of drug biotransformation?

    <p>Drug excretion unchanged</p> Signup and view all the answers

    What term refers to the products formed after drug metabolism?

    <p>Metabolite</p> Signup and view all the answers

    Which of the following statements is true regarding all drugs in relation to metabolism?

    <p>Some drugs do not undergo any metabolism.</p> Signup and view all the answers

    What characterizes a prodrug?

    <p>It needs to be metabolized to become active.</p> Signup and view all the answers

    Which phase of metabolic reaction does cytochrome P450 primarily mediate?

    <p>Oxidation/Reduction reactions</p> Signup and view all the answers

    What does Phase II metabolism aim to achieve?

    <p>Make drugs more hydrophilic for elimination.</p> Signup and view all the answers

    Why is the terminology of Phase I and Phase II reactions described as imprecise?

    <p>It suggests a strict order for metabolic reactions.</p> Signup and view all the answers

    What can polymorphisms in CYP450 enzymes lead to?

    <p>Variability in the speed of drug metabolism.</p> Signup and view all the answers

    What is a primary function of the CYP450 family of proteins?

    <p>To metabolize various compounds, including drugs.</p> Signup and view all the answers

    Why is understanding CYP polymorphisms increasingly important in drug development?

    <p>To customize and improve treatment effectiveness.</p> Signup and view all the answers

    How do Phase I and Phase II reactions relate to each other in drug metabolism?

    <p>They occur independently of one another.</p> Signup and view all the answers

    What type of groups does Phase II metabolism typically add to drugs?

    <p>Large, hydrophilic groups</p> Signup and view all the answers

    What role do CYP450 polymorphisms play in drug therapy?

    <p>Influence individual responses to medications.</p> Signup and view all the answers

    Which statement accurately describes the role of CYP enzymes?

    <p>CYP enzymes can be constitutively active or influenced by compounds.</p> Signup and view all the answers

    What is the purpose of adding endogenous compounds in Phase II reactions?

    <p>To make the drug more soluble for renal elimination.</p> Signup and view all the answers

    What is the first pass effect associated with?

    <p>The initial metabolism of orally ingested drugs by the liver.</p> Signup and view all the answers

    Which of the following is NOT a common molecule added during Phase II reactions?

    <p>Cholesterol (Cholesterol conjugation)</p> Signup and view all the answers

    Which enzyme is NOT classified as a Phase I enzyme?

    <p>Glutathione conjugation</p> Signup and view all the answers

    What happens to a drug that goes through the first pass effect?

    <p>It may be destroyed or activated depending on its nature.</p> Signup and view all the answers

    What effect do most added groups (excluding methylation) have on drugs?

    <p>They increase drug solubility in plasma.</p> Signup and view all the answers

    Where are CYP enzymes predominantly located in the body?

    <p>Liver</p> Signup and view all the answers

    Which statement is true about the CYP enzymes' activity?

    <p>They can be induced or inhibited by various compounds.</p> Signup and view all the answers

    Which of the following best describes the function of esterase enzymes?

    <p>They hydrolyze ester drugs.</p> Signup and view all the answers

    Study Notes

    Drug Metabolism

    • The processes by which drugs are chemically altered by biochemical reactions within the body.
    • Also known as drug biotransformation.
    • The liver is the primary organ responsible for drug metabolism.
    • Drug metabolism can alter a compound's properties, leading to either beneficial, harmful, or ineffective outcomes.

    Drug Metabolism and Liposolubility

    • Many drugs are lipophilic (fat-loving), allowing them to easily cross cell membranes like those in the intestinal mucosa and target tissues.
    • However, this same property makes renal excretion difficult.
    • Drugs need to be made more hydrophilic (water-loving) to dissolve in the aqueous urine.
    • Not all drugs undergo metabolism, and some are eliminated from the body unchanged.

    Drug Metabolism Outcomes

    • Active drugs can be converted to inactive drugs.
    • Active drugs can be converted to a more active or less active metabolite, or even a toxic metabolite.
    • Inactive prodrugs can be converted into their active therapeutic form.
    • Non-excretion-ready drugs can be converted into metabolites that are easier to excrete.

    Prodrugs

    • Prodrugs are inactive compounds that are metabolized and activated within the body.
    • Example: Plavix® (clopidogrel)

    Drug Metabolism Reactions

    • Two main classes of metabolic reactions:
      • Oxidation/Reduction reactions (Phase I)
        • Mediated by cytochrome P450 enzymes.
        • Primarily occurs in the liver.
      • Conjugation/Hydrolysis reactions (Phase II)
        • Adding a large, hydrophilic group to the drug molecule.
        • Makes the drug more amenable for elimination.

    Phase I and Phase II

    • "Phase I" and "Phase II" terms are imprecise and do not indicate a sequential order of reactions.
    • A drug can undergo a Phase II reaction without first going through a Phase I reaction.

    Cytochrome P450 (CYP) Enzymes

    • A large family of proteins with varying specializations for metabolizing different compounds.
    • Most drugs are metabolized by a limited number of CYPs.

    Polymorphisms in CYP Enzymes

    • Individual variations in CYP genes can result in either fast or slow drug metabolism.
    • Identifying these polymorphisms in patients is important for safe and effective drug treatment.
    • This is crucial for personalized medicine and drug development.

    Major CYP Families

    • Three main mammalian families involved in drug (xenobiotic) metabolism:
      • CYP1
      • CYP2
      • CYP3

    CYP Enzyme Induction and Inhibition

    • Some CYP enzymes have constitutive activity, while others are inducible or inhibitable by various compounds.
    • Induction refers to an increase in enzyme expression.

    Other Phase I Enzymes

    • Alcohol/aldehyde dehydrogenation
    • Decarboxylation
    • (Aldehyde) reductases
    • Hydrolysis enzymes: Esterases (hydrolyze ester drugs)

    Phase II Reactions

    • CYPs provide a reactive subunit for endogenous transferases (Phase II reactions).
    • Transferases add endogenous compounds to the drug or its metabolite.
    • Common molecules transferred/added in Phase II reactions:
      • Glucose (Glucuronidation)
      • Acetate (acetylation)
      • Glycine (Glycine conjugation)
      • Sulfate (Sulfate conjugation)
      • Glutathione (Glutathione conjugation)
      • Methyl groups (N-, O-, and S-methylation)

    Phase II Outcomes

    • Most additions (except methylation) increase the drug's solubility in plasma, promoting renal elimination.
    • Multiple transporters recognize the conjugates, allowing for active transport of drugs out of the system.

    Hepatic Metabolism

    • The liver is the primary site of drug metabolism.
    • The liver receives blood from the digestive tract before it flows to the heart.
    • This explains the "first-pass effect," where a drug can be deactivated or activated upon its first passage through the liver.

    First-Pass Effect

    • Oral medications can undergo the first-pass effect.
    • This must be considered in drug design and pharmaceutics.

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