Drug Interactions and Pharmacokinetics
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Questions and Answers

What occurs during a drug interaction characterized by altered absorption?

  • The distribution of both drugs in the body remains unchanged.
  • The enzyme activity of the precipitant drug is diminished.
  • The object's therapeutic effect increases due to improved solubility.
  • The object drug's bioavailability is altered due to the presence of the precipitant drug. (correct)

    • Which type of drug interaction is most likely to involve competition for binding sites on plasma proteins?

  • PK interactions
  • PD interactions
  • Protein displacement interactions (correct)
  • Pharmaceutical interactions

    • In the context of drug metabolism inhibition, which of the following statements is true?

  • All drugs act as inducers of enzyme activity.
  • Inhibition of metabolism affects only the therapeutic agents.
  • Inhibition often leads to increased blood concentrations of the victim drug. (correct)
  • Inhibition results in a decreased half-life of the precipitant drug.

    • What is a common consequence of drug-induced mucosal damage?

    <p>Increased risk of infection by normal flora</p> Signup and view all the answers

    Which interaction is most likely to result in a synergistic effect between two drugs?

    <p>Two drugs with similar therapeutic outcomes are combined.</p> Signup and view all the answers

    Which of these scenarios exemplifies an altered distribution interaction?

    <p>Two drugs compete for the same plasma protein binding site.</p> Signup and view all the answers

    In the context of pharmacogenetic interactions, which statement is true?

    <p>Individual genetic variations can significantly influence drug metabolism.</p> Signup and view all the answers

    How can dietary components lead to drug-food interactions?

    <p>Inhibiting the action of drug transport proteins.</p> Signup and view all the answers

    Which of the following statements about the interaction between clarithromycin and digoxin is true?

    <p>Clarithromycin alters the GI flora, allowing more digoxin to be absorbed.</p> Signup and view all the answers

    What is the primary consequence of increased GI motility on drug absorption?

    <p>It decreases the overall bioavailability of slowly absorbed drugs.</p> Signup and view all the answers

    Which of the following drugs is known to slow GI motility?

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

    How does drug-induced mucosal damage affect the absorption of certain drugs?

    <p>It may reduce absorption due to damage to the intestinal mucosa.</p> Signup and view all the answers

    Which mechanism most accurately describes the effect of anticholinergics on drug absorption?

    <p>They lead to delayed gastric emptying, which may slow drug absorption.</p> Signup and view all the answers

    Which of the following drugs can lead to alterations in intestinal blood flow, thereby inhibiting drug metabolism?

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

    What is a key characteristic of drugs that may cause clinically significant protein displacement interactions?

    <p>Narrow therapeutic index</p> Signup and view all the answers

    Which of the following combinations exemplifies a situation where protein binding is affected, potentially impacting drug efficacy?

    <p>Phenytoin + VPA</p> Signup and view all the answers

    Which drug acts as a competitive inhibitor of CYP1A2 while being metabolized by CYP2D6?

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

    Which drug is known to displace warfarin from plasma proteins, thus increasing its anticoagulant effects?

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

    What effect can acute inhibition of drug metabolism by certain drugs have on hypertension when albuterol is involved?

    <p>Increases hypertensive response</p> Signup and view all the answers

    Which of the following statements about CYP2D6 is accurate?

    <p>It is absent in 5 to 10% of Caucasians.</p> Signup and view all the answers

    Which of the following drugs is an example of a substrate for more than one enzyme?

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

    What is the result of a drug displacing another from protein binding sites in terms of pharmacokinetics?

    <p>Increased free concentration of the displaced drug</p> Signup and view all the answers

    Which drug is an inducer of CYP1A2 and an inhibitor of CYP2C19?

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

    What is the most likely consequence of co-administering a drug that induces metabolic enzymes like phenytoin with warfarin?

    <p>Potential bleeding risk if adjustments are not made</p> Signup and view all the answers

    Which statement accurately reflects the action of enzyme inhibitors compared to inducers?

    <p>Inhibitors often cause maximal effect within 24 hours</p> Signup and view all the answers

    What occurs when an enzyme inducer drug is discontinued while the patient is on an interacting object drug?

    <p>Delayed reversal of enzyme induction, potentially affecting drug efficacy</p> Signup and view all the answers

    In the context of drug metabolism, how does phenobarbital affect warfarin levels?

    <p>It induces warfarin metabolism, decreasing its effectiveness</p> Signup and view all the answers

    What is a key mechanism of drug-drug interactions affecting renal excretion?

    <p>Competition for active tubular secretion</p> Signup and view all the answers

    Which of the following best describes the interaction between erythromycin and theophylline?

    <p>Erythromycin inhibits the metabolism of theophylline, raising its levels</p> Signup and view all the answers

    What is the impact of competitive inhibition within active tubular secretion systems?

    <p>Decreased secretion of one or both drugs due to saturation</p> Signup and view all the answers

    Which of the following factors is NOT involved in renal drug elimination interactions?

    <p>Inhibition of intestinal flora</p> Signup and view all the answers

    How does the effect of an enzyme inhibitor interact with an enzyme inducer when administered together?

    <p>The effect of the inhibitor prevails, reducing drug metabolism</p> Signup and view all the answers

    What is the significance of the half-life (t1/2) in relation to enzyme inhibitors?

    <p>Inhibition effects are maximal usually within 3 t1/2</p> Signup and view all the answers

    Which mechanism of drug interaction is most likely to alter the absorption of a drug by changing the composition of bacteria in the GIT?

    <p>Alteration of intestinal flora</p> Signup and view all the answers

    How might drug-induced mucosal damage impact the absorption of medications?

    <p>By leading to a reduced surface area for absorption</p> Signup and view all the answers

    What is the result of a drug that inhibits drug metabolism in the intestinal cells?

    <p>Decreased drug absorption and potentiated effects</p> Signup and view all the answers

    Which of the following factors most likely affects drug absorption through inhibition of GI motility?

    <p>Delayed gastric emptying</p> Signup and view all the answers

    How does protein displacement interaction typically affect drug absorption?

    <p>It causes an increase in bioavailability of the displaced drug</p> Signup and view all the answers

    What effect does cholestyramine have on the absorption of thyroxine?

    <p>It decreases thyroxine absorption</p> Signup and view all the answers

    What influence do antacids have on the absorption of weak acidic drugs like ketoconazole?

    <p>Antacids decrease gastric pH, reducing absorption</p> Signup and view all the answers

    What impact does antibiotic administration have on gut absorption?

    <p>It decreases the number of bacteria that can affect drug absorption</p> Signup and view all the answers

    Which effect can antacids have on drugs administered concurrently, such as ciprofloxacin?

    <p>They can reduce the absorption of antibiotics</p> Signup and view all the answers

    Which scenario would likely impair drug absorption due to altered gastric pH?

    <p>Administration of a strong antacid with a weak acidic drug</p> Signup and view all the answers

    Study Notes

    Drug Interactions

    • Drug interactions are when one drug's effects are modified by another drug given before or at the same time.
    • This modification can happen through pharmacokinetic (PK) or pharmacodynamic (PD) interactions.

    Pharmacokinetic Interactions

    • Occur when: absorption, distribution, metabolism, or excretion of a drug is altered.
    • Affected by:
      • Absorption:
        • Complexation or chelation
        • Alteration of gastric pH
        • Adsorption
        • Alteration of intestinal flora
        • Alteration of GI motility
        • Drug-induced mucosal damage
        • Inhibition of drug metabolism in intestinal cells
      • Distribution:
        • Protein displacement
        • Tissue binding
      • Metabolism:
        • Enzyme induction
        • Enzyme inhibition
      • Excretion:
        • Competition for active tubular secretion
        • pH-dependent renal tubular transport
        • Increased renal blood flow

    Pharmacodynamic Interactions

    • Produce:
      • Antagonistic (opposing) effects
      • Synergistic (enhanced) effects
      • Additive (combined) effects

    Other Interactions

    • Pharmacogenetic interactions: Occurs when the PK effect of a drug is changed by genetic factors affecting metabolism
    • Pharmaceutical interactions: Caused by chemical or physical incompatibility when mixing drugs.

    Important Definitions

    • Precipitant (or perpetrator) drug: The drug causing the interaction.
    • Object (or victim) drug: The drug being affected by the interaction.
    • Substrate: The drug metabolized by a specific enzyme.
    • Inhibitors: Compounds that block the action of an enzyme or transport protein.
    • Inducers: Compounds that stimulate the action of an enzyme or transport protein.

    Examples of Drug Interactions

    • Antacids: Antacids like sodium bicarbonate can increase gastric pH, delaying absorption of drugs like ketoconazole and decreasing its effectiveness.
    • Tetracycline: When combined with iron preparations or milk, tetracycline forms complexes that are poorly absorbed.
    • Ciprofloxacin: Antacids and sucralfate decrease its absorption significantly; administration should be at least 2 hours apart.
    • Digoxin: Erythromycin and clarithromycin may increase digoxin absorption by changing intestinal flora.
    • Metoclopramide: Increases stomach emptying time, increasing cyclosporine absorption, but decreasing digoxin absorption.

    Avoiding and Managing Drug Interactions

    • Understand the mechanisms of interaction and how they affect drug absorption, distribution, metabolism, and excretion.
    • Use tools like drug interaction databases to identify potential risks.
    • Monitor patients carefully for signs of drug interaction.
    • Adjust dosages or consider alternative medications if necessary.
    • Inform patients about potential interactions, including interactions with food, alcohol, and herbal products.
    • Ensure proper administration timing and routes for interacting medications.
    • Be aware of individual patient factors like age, genetics, and co-morbidities that could increase the risk of drug interaction.

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    Pharma - 113 Drug Interactions PDF

    Description

    Explore the various types of drug interactions and their impact on pharmacokinetics. This quiz covers the mechanisms of how absorption, distribution, metabolism, and excretion of drugs can be altered by other substances. Test your understanding of these critical pharmaceutical concepts.

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