Pharmacology Chapter on Angiotensin II and Toxicity
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Questions and Answers

What is the primary factor determining whether a substance has beneficial effects or becomes toxic?

  • Time period of exposure to the substance
  • Chemical structure of the substance
  • Concentration or dose of the substance (correct)
  • Rate of absorption in the body
  • What does the therapeutic index (TI) evaluate in drug administration?

  • The purity of the drug compound
  • The ratio of LD50 to ED50 or TD50 to ED50 (correct)
  • The duration of the drug's effects
  • The maximum effect of a drug on a target
  • At high concentrations, which receptor type does angiotensin II primarily bind to, leading to the inhibition of vasoconstriction?

  • ATR Type 1 Receptor
  • ATR Type 2 Receptor (correct)
  • ATR Type 3 Receptor
  • ATR Type 4 Receptor
  • What does the term LD50 represent in pharmacology?

    <p>The amount needed to kill 50% of test cells or organisms</p> Signup and view all the answers

    Which of the following substances can lead to toxicity at high concentrations, despite being beneficial at lower doses?

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

    In the context of therapeutic index, what does a low TI indicate?

    <p>Close proximity of therapeutic and toxic dose ranges</p> Signup and view all the answers

    What is the consequence of a drug having a large therapeutic index?

    <p>Lower likelihood of toxicity occurring</p> Signup and view all the answers

    What type of antagonism can be directly defined as one substance acting to counteract the effects of another substance?

    <p>Physiological antagonism</p> Signup and view all the answers

    Which type of agonist can produce a maximum biological response at certain doses?

    <p>Full agonist</p> Signup and view all the answers

    What is the primary characteristic of a partial agonist?

    <p>It cannot elicit a complete response, regardless of dose.</p> Signup and view all the answers

    How is the therapeutic index defined in pharmacology?

    <p>The ratio of the toxic dose to the effective dose of a drug.</p> Signup and view all the answers

    Which scenario best describes pharmacokinetic antagonism?

    <p>One drug affects the metabolism of another drug.</p> Signup and view all the answers

    What does EC50 represent in pharmacological terms?

    <p>The concentration required to elicit 50% of the maximum biological response.</p> Signup and view all the answers

    What aspect of drug selectivity refers to the ability of a drug to produce a particular effect based on its molecular structure?

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

    How does drug promiscuity potentially benefit pharmacology?

    <p>It allows drugs to interact with multiple targets for diverse therapeutic effects.</p> Signup and view all the answers

    What defines drug potency in relation to its effect?

    <p>The amount of drug required to elicit a specific effect.</p> Signup and view all the answers

    In what scenario might a drug with high selectivity cause unintended harmful effects?

    <p>When it interacts with non-target receptors due to promiscuity.</p> Signup and view all the answers

    What is indicated by a high therapeutic index of a drug?

    <p>There is a large margin between effective dose and toxic dose.</p> Signup and view all the answers

    Which statement exemplifies physiological antagonism in pharmacology?

    <p>Two drugs act at different receptor sites to produce opposing effects.</p> Signup and view all the answers

    What factor primarily influences the amount of a drug needed to achieve its effect?

    <p>The affinity of the drug for its target.</p> Signup and view all the answers

    Which of the following represents a potential toxic effect resulting from drug promiscuity?

    <p>Unintended receptor interactions leading to bronchospasm.</p> Signup and view all the answers

    Study Notes

    Angiotensin II

    • At low concentrations, Angiotensin II binds to the Angiotensin II Type 1 receptor (ATR1), leading to vasoconstriction
    • At very high concentrations, it binds to the Angiotensin II Type 2 receptor (ATR2), negating the effects of ATR1 activation
    • Angiotensin II has a high affinity for ATR1 and a low affinity for ATR2, explaining why it only binds to ATR2 at very high concentrations

    Toxicity

    • Everything is toxic, the dose determines if it has a beneficial or toxic effect
    • Insulin at high concentrations can lead to diabetic hypoglycemia and death
    • Paracetamol, an analgesic, at high concentrations can kill liver and kidney cells

    LD50 and TD50

    • LD50: The amount of a drug needed to kill 50% of test cells or organisms
    • TD50: The amount of a drug needed to cause toxicity in 50% of test cells or organisms
    • Toxic effect can involve dysfunction or cell death

    Therapeutic Index

    • Therapeutic index (TI) = LD50 or TD50/ED50, indicating the likelihood of side effects or toxicity
    • Drugs with a low TI (blue and red lines close together) require careful dosing as toxicity can occur at therapeutic doses, like Warfarin
    • Drugs with a large TI, therapeutic concentrations are much lower than toxic ones, reducing the likelihood of toxicity

    Drug Properties

    • Three key drug properties determine if a drug works and works safely:
      • Selectivity/Specificity
      • Potency
      • Efficacy

    Selectivity/Specificity

    • Selectivity describes a drug's ability to produce a particular effect, relating to its molecular structure and receptor specificity
    • Receptor specificity is determined by the precise molecular interactions between a drug molecule and a receptor protein
    • Some drugs bind to one target (e.g., a receptor), while others interact with multiple targets
    • Binding to multiple targets (promiscuity) can be beneficial pharmacologically or lead to off-target/toxic effects

    Drug Promiscuity

    • Example 1: Statins
      • Inhibit HMG-CoA reductase, reducing cholesterol synthesis in the liver and circulating cholesterol levels
      • Reported to modulate nitric oxide synthase gene expression in vascular endothelial cells (promoting vasodilation), reducing macrophage proliferation (anti-atherosclerosis effects), and inflammatory markers (anti-thrombus formation effects)
    • Example 2: Propranolol
      • Blocks beta-adrenoceptor beta 1 in the heart, reducing heart rate and contractive force (clinical effect)
      • Also blocks beta-adrenoceptor beta 2, inhibiting bronchial smooth muscle relaxation, potentially causing bronchospasm in asthmatic and COPD patients (toxic/harmful effect)

    Drug Potency

    • Relates to the amount of drug needed to elicit an effect
    • Depends on the drug's affinity for its target
      • Low affinity: Weak binding, readily dissociates, requires larger amounts of drug for effect
      • High affinity: Strong binding, requires less drug for effect
    • Potency is often expressed as EC50, the concentration needed to elicit 50% of the maximum response
    • Time of exposure is crucial, especially in cell culture experiments

    Drug Efficacy

    • Ability of a drug to induce a biological or physiological response
    • Drugs can be:
      • Full agonists: Induce a full biological response at specific doses
      • Partial agonists: Cannot induce a full biological response regardless of dose, but can still be effective drugs with reduced overdose risk
    • ED50: Dose of drug needed for a therapeutic effect in 50% of test cells or organisms

    Agonists and Antagonists

    • Agonist: A compound that binds to a target molecule (e.g., a receptor) and activates it, eliciting a response.
    • Antagonist: A compound that binds to a target molecule and inhibits its activity.

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    Description

    This quiz explores the pharmacology of Angiotensin II, its receptors, and the principles of toxicity, including LD50 and TD50 values. Understand how different concentrations can lead to beneficial or harmful effects in various substances. Test your knowledge on the therapeutic index and its implications on drug safety.

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