PCT312 Pharmacology I - Week 3
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Questions and Answers

What is the primary role of clearance in pharmacology?

  • To measure the rate of drug metabolism
  • To assess the drug's therapeutic effects
  • To determine the efficiency at which a drug is removed from the body (correct)
  • To establish the half-life of a drug

    • Which factor does NOT affect the rate of drug elimination?

  • Kidney function
  • Rate of administration
  • Molecular weight of the drug (correct)
  • Liver function

    • How many half-lives are typically required to reach a steady state for a first-order process?

  • 8-9 half-lives
  • 6-7 half-lives
  • 4-5 half-lives (correct)
  • 2-3 half-lives

    • What does 'Css' refer to in pharmacology?

    <p>The steady-state drug concentration</p> Signup and view all the answers

    Which route accounts for the primary excretion of drugs from the body?

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

    Which statement best describes glomerular filtration in drug excretion?

    <p>It primarily excludes protein-bound drugs.</p> Signup and view all the answers

    What factor increases the amplitude of fluctuations in drug concentration?

    <p>Using larger doses at shorter intervals</p> Signup and view all the answers

    What effect does probenecid have on the secretion of penicillins and other weak acids?

    <p>It inhibits the secretion of these drugs.</p> Signup and view all the answers

    What occurs during proximal tubular secretion in drug excretion?

    <p>Transport primarily occurs through two energy-requiring systems</p> Signup and view all the answers

    What is the primary purpose of manipulating urine pH in drug clearance?

    <p>To minimize back diffusion and increase clearance.</p> Signup and view all the answers

    What process is referred to as 'ion trapping' in drug elimination?

    <p>The manipulation of urine pH to affect ionization.</p> Signup and view all the answers

    Which statement about biliary excretion is correct?

    <p>It favors the elimination of compounds with high molecular weight.</p> Signup and view all the answers

    What is the significance of enterohepatic cycling in drug metabolism?

    <p>It allows excreted conjugated drugs to be reabsorbed.</p> Signup and view all the answers

    What does 'total body clearance' refer to?

    <p>The volume of body fluid from which a drug is completely removed per unit time.</p> Signup and view all the answers

    When is renal clearance approximately equal to creatinine clearance?

    <p>When drugs are primarily eliminated via glomerular filtration.</p> Signup and view all the answers

    What happens to weak acids like phenobarbital or aspirin if the urine is alkalinized?

    <p>They remain ionized and are less reabsorbed.</p> Signup and view all the answers

    What characterizes a full agonist?

    <p>It has high efficacy and produces maximal effects.</p> Signup and view all the answers

    What is the primary role of an antagonist in drug-receptor interactions?

    <p>To block a receptor and prevent the action of an agonist.</p> Signup and view all the answers

    How does an inverse agonist affect signal transduction?

    <p>It decreases the rate of signal transduction.</p> Signup and view all the answers

    Which receptor family is associated with ligand-gated ion channels?

    <p>Ligand-gated ion channels.</p> Signup and view all the answers

    What factor does NOT influence the potency of an agonist?

    <p>Rate of receptor recycling.</p> Signup and view all the answers

    What does a renal drug clearance higher than the creatinine clearance indicate?

    <p>The drug undergoes tubular secretion.</p> Signup and view all the answers

    What is the purpose of a loading dose?

    <p>To rapidly achieve desired plasma drug levels.</p> Signup and view all the answers

    Which formula is used to calculate maintenance dose?

    <p>Maintenance Dose = Rate of drug elimination × Dosage interval</p> Signup and view all the answers

    What does a renal drug clearance lower than the creatinine clearance suggest?

    <p>The drug binds well to plasma proteins or is reabsorbed.</p> Signup and view all the answers

    What does the therapeutic index indicate?

    <p>The range between the effective dose and the toxic dose.</p> Signup and view all the answers

    What defines potency in pharmacodynamics?

    <p>The concentration of a drug needed to produce a specific effect.</p> Signup and view all the answers

    Which of the following is NOT considered a main target of drug action?

    <p>Plasma lipids</p> Signup and view all the answers

    What is the role of drug receptors?

    <p>To bind drugs and mediate their pharmacologic actions.</p> Signup and view all the answers

    Study Notes

    PCT312 Pharmacology I (Week 3)

    • General Pharmacology - Pharmacokinetics & Pharmacodynamics
    • Focuses on the concepts of plasma steady state and clearance.
    • Importance of half-life (t1/2):
      • Determines frequency of dosing
      • Estimates time to reach steady state
      • Estimates time needed for drug removal after stopping
    • Steady State:
      • Initial administration rate is much higher than elimination rate, leading to low plasma concentration.
      • As administration continues, elimination rate increases, while administration rate remains constant.
      • Eventually, elimination rate equals administration rate, and a steady-state equilibrium is achieved
      • Time to reach steady state is roughly 4-5 half-lives.
    • Factors affecting steady state:
      • Admin rate/dose
      • Rate of elimination (e.g., liver/kidney function)
    • Drug Excretion:
      • Primarily through urine, but also via bile, sweat, saliva, tears, feces, breast milk, and exhaled air.
    • Glomerular filtration:
      • Rate (GFR) is 90-120 mL/min
      • Affected by renal disease
      • Lipid solubility and pH don't influence passage.
      • Drug binding to proteins can affect filtration.
    • Proximal tubular secretion:
      • Energy-requiring active transport systems for anions and cations
    • Distal tubular reabsorption:
      • Drug concentration increases as passing distal tubule
      • If uncharged, drug may diffuse out back into blood.
      • pH manipulation (ion trapping) can influence drug elimination.
    • Total Body Clearance (Cl):
      • Volume of body fluid (blood/plasma) eliminating a drug per unit of time
      • Factors include intestines, bile, lungs, and breast milk
      • CLtotal = CLhepatic + CLrenal + CLpulmonary + CLother
    • Biliary excretion:
      • Favors compounds with high molecular weight
      • Conjugation (e.g., with glucuronate) enhances biliary excretion
      • Enterohepatic cycling (reabsorption and return to liver) is possible.
    • Renal Clearance:
      • Clearance rates can be used to assess a drug's renal elimination.
      • Clearance = 100ml/min with normal kidneys
    • Dosage calculations:
      • Loading dose: Used to obtain desired plasma levels rapidly (e.g., serious infections)
      • Maintenance dose: Administered to maintain a desired steady-state plasma concentration
      • Rate of drug elimination = average Css × Cl / dosage interval

    Pharmacodynamics

    • Definition: Study of the biological and therapeutic effects of drugs (how drugs affect the body).
    • Main Targets for Drug Action:
      • Receptors
      • Ion channels
      • Enzymes
      • Carrier molecules
    • Drug Receptors: Sensing elements, usually macromolecules. Binding initiates a series of events leading to physiological effect. The magnitude of response is proportional to the number of drug-receptor complexes
    • Agonists: drugs that stimulate receptors to initiate changes in cell function (e.g. increasing or decreasing cell signaling).
    • Antagonists: drugs that bind to receptors without eliciting a response, blocking the action of agonists.
    • Drug-receptor classification:
      • Ligand-gated ion channels, G protein-coupled receptors, enzyme-linked receptors, intracellular receptors

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    PCT312 Pharmacology I Week 3 PDF

    Description

    Dive into the critical concepts of pharmacokinetics and pharmacodynamics in this quiz for Pharmacology I. Understand plasma steady state, clearance, and the significance of half-life in determining drug dosing and elimination. Explore the factors affecting the steady state and the various methods of drug excretion.

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