Drug Metabolism
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Questions and Answers

What is one of the factors that could cause significant changes in biological activity of a drug?

  • Smell of the drug
  • Color of the drug
  • 3D shape of the molecule (correct)
  • Size of the drug particles

    • How was the initial receptor model based on the interaction between drugs and receptors?

  • Lock-and-key concept (correct)
  • Maze concept
  • Jigsaw puzzle concept
  • Musical chairs concept

    • What can happen when a drug docks with a receptor based on the text?

  • The receptor remains rigid
  • The drug undergoes adjustment
  • The receptor undergoes an adjustment in 3D structure (correct)
  • The receptor loses its 3D structure

    • How is the drug-receptor association depicted in the text?

    <p>Continuous process</p> Signup and view all the answers

    What is the significance of the first-pass effect mentioned in the text?

    <p>It decreases the bioavailability of drugs administered orally.</p> Signup and view all the answers

    Why is lidocaine impractical to administer orally?

    <p>Over 60% of it is metabolized during its first pass through the liver.</p> Signup and view all the answers

    How does the rapid metabolism of lidocaine benefit patients with cardiac arrhythmias?

    <p>It decreases toxic responses by converting lidocaine into inactive metabolites.</p> Signup and view all the answers

    What development was inspired by the understanding of the metabolic labile site on lidocaine?

    <p>Development of primary amine analog tocainide.</p> Signup and view all the answers

    What does the pKa measure?

    <p>Extent to which the acid reacts with water</p> Signup and view all the answers

    Where does the equilibrium lie for a strong acid in water?

    <p>To the right</p> Signup and view all the answers

    What does a high pKa value indicate about a weak acid in water?

    <p>Lies to the left in equilibrium</p> Signup and view all the answers

    What does a pKa for a base actually represent?

    <p>The pKa of the conjugate acid of the base</p> Signup and view all the answers

    What is the relationship between pH and percent ionization of an HA acid when the pH is 1 unit greater than the pKa?

    <p>99% ionized</p> Signup and view all the answers

    How does an increase of 2 pH units affect the ionization of a BH+ acid?

    <p>99% nonionized</p> Signup and view all the answers

    What is the impact of increasing the hydrogen ion concentration on drug equilibrium?

    <p>Increases the conjugate base concentration</p> Signup and view all the answers

    At what pH value would an HA acid be 50% ionized?

    <p>pKa + 1</p> Signup and view all the answers

    Why is it impractical to administer lidocaine orally?

    <p>It undergoes rapid metabolism in the liver during the first pass effect.</p> Signup and view all the answers

    What happens to lidocaine when administered intravenously for cardiac arrhythmias?

    <p>It is rapidly biotransformed to inactive metabolites.</p> Signup and view all the answers

    What is a significant characteristic of lidocaine's first-pass effect?

    <p>Over 60% of it is metabolized during its initial passage through the liver.</p> Signup and view all the answers

    What led to the development of tocainide according to the text?

    <p>Understanding the metabolic labile site on lidocaine.</p> Signup and view all the answers

    Which factor contributes to the drug-receptor interaction process by favoring the desired pharmacological response?

    <p>Good ability of the drug to fit the receptor</p> Signup and view all the answers

    Why are second-generation antihistamines like fexofenadine claimed to cause less sedation?

    <p>They do not readily penetrate the blood-brain barrier</p> Signup and view all the answers

    What happens when a drug binds poorly to a receptor according to the text?

    <p>Reverse reaction and reduced pharmacological effect</p> Signup and view all the answers

    Why do nonsteroidal anti-inflammatory drugs sometimes cause discomfort and ulceration in the gastrointestinal mucosa?

    <p>They combine with undesired cyclooxygenase receptors in the gastrointestinal mucosa</p> Signup and view all the answers

    What is the primary amine form of the carboxylic acid at physiological pH?

    <p>50% protonated and 50% in the free amine form</p> Signup and view all the answers

    Why is adjusting the pH of phenytoin injection to 12 necessary?

    <p>To achieve complete ionization</p> Signup and view all the answers

    What percentage of the drug is in the ionized form at pH 12?

    <p>99.98%</p> Signup and view all the answers

    Why is an alkaline solution with a pH of 12 generally not administered with other intravenous fluids?

    <p>It can cause patient irritation</p> Signup and view all the answers

    What is the importance of understanding the 3D shape of a drug molecule, according to the text?

    <p>It can lead to significant changes in the drug's biological activity.</p> Signup and view all the answers

    Why is the lock-and-key concept of drug-receptor interaction considered outdated?

    <p>It doesn't account for the flexibility of both the drug and receptor.</p> Signup and view all the answers

    What effect can drug-receptor association have on macromolecules, as mentioned in the text?

    <p>It may alter the configuration of macromolecules for agonist responses.</p> Signup and view all the answers

    Why are slight structural variations in drugs significant, according to the text?

    <p>They may increase or decrease the drug's biological activity.</p> Signup and view all the answers

    Acids are defined as proton acceptors and bases are defined as proton donors.

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

    Water can act as an acid by donating a proton to a basic drug.

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

    Ionized acids, like carboxylic acids, donate their protons forming ionized conjugate acids.

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

    A drug's acid–base properties do not influence its biodistribution and partitioning characteristics.

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

    During the initial trip through the liver, a significant proportion of a drug will be transported to the kidneys for excretion.

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

    Lidocaine is an example of a drug that undergoes rapid metabolism during the first-pass effect.

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

    The first-pass effect of lidocaine makes it practical to administer orally.

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

    The understanding of the metabolic labile site on lidocaine led to the development of a similar drug called lidocainide.

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

    Phenytoin injection must be adjusted to pH 10 to ensure complete ionization and maximize water solubility.

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

    At pH 12, 99.0% of the drug phenytoin will be in the insoluble acid form.

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

    A highly alkaline solution with a pH of 12 can be easily administered with other intravenous fluids buffered at pH 7.4.

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

    Lowering the pH of phenytoin solution would result in the parent unionized phenytoin precipitating out of solution.

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

    An increase of 1 pH unit from the pKa value will cause a BH+ acid to be 90.9% in the ionized form.

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

    In the Henderson-Hasselbalch equation, when log [conjugate base] / [acid] = 1, the pH is equal to pKa.

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

    Increasing the hydrogen ion concentration (decreasing the pH) will shift the equilibrium to the right for both HA acids and BH+ acids.

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

    An increase of 2 pH units essentially shifts an HA acid to complete ionization (99%) and a BH+ acid to the nonionic conjugate base form (0.99%).

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

    Why is Tropicamide buffered near pH 4 for eye drop administration?

    <p>To maximize water solubility</p> Signup and view all the answers

    Why are local anesthetic eye drops sometimes used along with Tropicamide eye drops?

    <p>To minimize patient discomfort</p> Signup and view all the answers

    In what pH range is indomethacin stabilized to prevent instability issues?

    <p>pH 4-5</p> Signup and view all the answers

    Why is only 50% of indomethacin in the water-soluble form when administered as a suspension at pH 4-5?

    <p>Due to its proximity to the drug's pKa</p> Signup and view all the answers

    Why is the intravenous dosage form of indomethacin prepared as a sodium salt?

    <p>To increase water solubility</p> Signup and view all the answers

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