Pharmacology: Drug Targets and Side Effects
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Questions and Answers

What is an example of an 'on-target' side effect caused by opioid analgesic drugs?

  • Constipation (correct)
  • Drowsiness
  • Headache
  • Nausea

    • Off-target side effects are always mediated by the same receptor as the desired drug effect.

    False

    What is the primary constituent of dimenhydrinate known for its antiemetic effect?

    Diphenhydramine

    Dramamine is marketed under the brand name _____ in Canada.

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

    Match the drug with its respective side effect:

    <p>Dimenhydrinate = Drowsiness Opioid analgesics = Constipation Diphenhydramine = Anti-emetic effect Antihistamines = Allergies</p> Signup and view all the answers

    What property of a drug determines its ability to produce a biological effect once it is bound to a receptor?

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

    Antagonists have high efficacy.

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

    What is the EC50 of a drug?

    <p>The concentration of a drug required to produce 50% of its maximal effect.</p> Signup and view all the answers

    Fentanyl is a full agonist that selectively binds to the ______ receptor.

    <p>μ-opioid</p> Signup and view all the answers

    Match the following terms to their definitions:

    <p>Affinity = Tendency of a drug to bind to receptors Efficacy = Ability of a drug to activate a receptor once bound Potency = Concentration required to produce 50% of maximal effect pEC50 = Negative logarithm of the EC50 value</p> Signup and view all the answers

    Which drug is a competitive non-selective antagonist at opioid receptors?

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

    A higher EC50 value indicates a more potent drug.

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

    If a drug has a pEC50 of 6.0, what is the EC50?

    <p>10^-6 M</p> Signup and view all the answers

    What does Emax represent in pharmacology?

    <p>The maximal response a drug can produce</p> Signup and view all the answers

    Drugs with high potency always have high efficacy.

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

    What is the significance of EC50 in pharmacology?

    <p>It indicates the concentration needed to produce 50% of the maximal response.</p> Signup and view all the answers

    A drug with low affinity but high efficacy is effective even when only a few receptors are ______.

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

    What does the efficacy (Emax) of a drug represent?

    <p>The maximum effect that can be expected from the drug</p> Signup and view all the answers

    As drug concentration increases, the response usually decreases.

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

    Match the following terms with their descriptions:

    <p>Efficacy = The maximal response a drug can produce Potency = The concentration of drug needed for a specific effect Affinity = The strength of binding between a drug and its receptor Receptor Reserve = Excess receptors available beyond those needed for a maximal effect</p> Signup and view all the answers

    What is the characteristic shape of dose-response curves typically described as?

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

    A drug with zero efficacy has an efficacy value of _______.

    <p>0</p> Signup and view all the answers

    Match the drug characteristics with their definitions:

    <p>Emax = Maximum drug effect Full Agonist = Strongly activates receptor Partial Agonist = Moderately activates receptor No Efficacy = No receptor activation tendency</p> Signup and view all the answers

    What occurs when the stimulus to a cell exceeds its maximal capability?

    <p>The fluid escapes through the overflow</p> Signup and view all the answers

    Dose-response curves can be both linear and semilogarithmic.

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

    What physiological response is commonly measured when assessing drug effects?

    <p>Increase in heart rate, rise in blood pressure, or contraction of smooth muscle.</p> Signup and view all the answers

    What does the EC50 value approximate for a partial agonist?

    <p>The affinity for the agonist</p> Signup and view all the answers

    The concentration-effect curves can directly measure the binding affinity of full agonist drugs for their receptors.

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

    What is referred to as the concentration inducing a response halfway between baseline and maximum?

    <p>EC50</p> Signup and view all the answers

    If the maximal response to an agonist is lower than the system’s maximal response, then the concentration producing the maximal response approximates the ______ binding concentration of the agonist.

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

    Match the terms with their descriptions:

    <p>EC50 = Concentration producing 50% of the maximal response Receptor Reserve = Number of receptor sites exceeding signaling capacity Partial Agonist = A substance that activates a receptor but produces a weaker response Full Agonist = A substance that fully activates a receptor</p> Signup and view all the answers

    What happens to potency when there is a higher receptor reserve for most full agonists?

    <p>Increased apparent potency</p> Signup and view all the answers

    What physiological outcome may differ when two tissues express the same receptor with different reserve levels?

    <p>Impact of a set concentration of an agonist</p> Signup and view all the answers

    Occupying 10% of available receptor sites will produce a maximum response if there is a 10 to 1 ratio of receptor sites to signaling machinery.

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

    Which of the following describes a 'druggable genome'?

    <p>A subset of genes that express proteins able to bind drug-like molecules.</p> Signup and view all the answers

    Receptors and drug targets are the same entity in pharmacology.

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

    What is the main role of protein targets in drug binding?

    <p>To elicit a physiological effect by binding to drugs.</p> Signup and view all the answers

    The main challenge in drug development is identifying targets that play a meaningful role in the __________ process.

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

    Which of the following options is NOT considered a protein target for drug binding?

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

    Match the following types of drug targets with their descriptions:

    <p>Receptors = Recognize endogenous signals Enzymes = Catalyze biochemical reactions Transporters = Facilitate the movement of molecules Ion channels = Control the flow of ions across membranes</p> Signup and view all the answers

    Only proteins can act as drug targets in pharmacology.

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

    What determines a target's ability to discern differences in electronic structures during drug binding?

    <p>The target's three-dimensional structure.</p> Signup and view all the answers

    What effect does epinephrine have when it binds to the β adrenoceptor?

    <p>Increases the force and rate of the heartbeat</p> Signup and view all the answers

    Epinephrine is a selective agonist for all adrenergic receptors.

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

    What is the term used for drugs that activate receptors and elicit a tissue response?

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

    Binding of a drug to a receptor may or may not result in _____ of the receptor.

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

    Match the following terms with their definitions:

    <p>Agonists = Drugs that activate receptors Binding = Occupation of a receptor by a drug molecule Active conformation = State of a receptor that promotes signaling Inactive conformation = State of a receptor that does not promote signaling</p> Signup and view all the answers

    What physiological effect is NOT associated with the binding of epinephrine to β adrenoceptors?

    <p>Decreased respiratory rate</p> Signup and view all the answers

    What is the relationship between agonists and receptor conformation?

    <p>Agonists have a higher affinity for the active conformation of receptors.</p> Signup and view all the answers

    A competitive antagonist binds to the same site as an agonist but does not activate the receptor.

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

    What is the main effect of receptor antagonists?

    <p>They block the effect of agonists.</p> Signup and view all the answers

    Antagonists can cause receptor activation when they bind to their target receptors.

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

    What does the equilibrium constant KA represent?

    <p>The concentration of drug required to occupy 50% of the receptor sites at equilibrium.</p> Signup and view all the answers

    Agonists and antagonists are both types of __________, which can bind to receptors.

    <p>receptor ligands</p> Signup and view all the answers

    Match the drug types with their characteristics:

    <p>Agonist = Causes receptor activation Antagonist = Blocks receptor activation Receptor Ligand = Includes both agonists and antagonists Receptor Antagonist = Binds without activating the receptor</p> Signup and view all the answers

    What happens to the value of KA as the affinity of a drug for its receptor increases?

    <p>KA decreases</p> Signup and view all the answers

    For most drugs, the processes of binding and activation are considered irreversible.

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

    Define receptor antagonists.

    <p>Drugs that bind to receptors at the same site as agonists without causing activation, blocking their effects.</p> Signup and view all the answers

    What does efficacy in pharmacology refer to?

    <p>The drug's ability to activate a receptor once bound</p> Signup and view all the answers

    Potency is solely determined by the efficacy of a drug.

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

    What is the primary characteristic of antagonists regarding efficacy?

    <p>Zero efficacy</p> Signup and view all the answers

    The concentration producing 50% of the maximal response is known as ______.

    <p>EC50</p> Signup and view all the answers

    Which drug is identified as a competitive non-selective antagonist at opioid receptors?

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

    Match the following drugs with their properties:

    <p>Fentanyl = Full agonist Naloxone = Antagonist Drug A = Most potent drug Drug D = Least potent drug</p> Signup and view all the answers

    What does the term pEC50 represent?

    <p>Negative logarithm of the EC50 value</p> Signup and view all the answers

    A drug that binds with high affinity but has low efficacy can still produce a significant biological effect.

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

    What does the EC50 value approximate for a partial agonist?

    <p>Binding affinity</p> Signup and view all the answers

    The concentration of a drug that induces a response halfway between the baseline and maximum is referred to as the EC50.

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

    What phenomenon occurs when the number of receptor sites exceeds the signaling capacity of the cell?

    <p>Spare receptors</p> Signup and view all the answers

    In a 10 to 1 ratio of receptor sites to signaling machinery, occupying ___% of the available receptor sites will produce a maximum response.

    <p>10</p> Signup and view all the answers

    Which statement accurately describes the relationship between receptor reserve and potency for full agonists?

    <p>Higher receptor reserves typically lead to increased potency.</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>EC50 = Concentration producing 50% of the maximum effect Receptor reserve = Excess receptors compared to signaling machinery Partial agonist = Drug that activates a receptor but produces a less than full response Full agonist = Drug that activates a receptor with maximum response</p> Signup and view all the answers

    Concentration-effect curves can be used to measure the affinity of full agonist drugs for their receptors.

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

    What effect does the different reserve levels in two tissues expressing the same receptor have on the physiological outcomes?

    <p>Different physiological outcomes for the same concentration of agonist</p> Signup and view all the answers

    Study Notes

    Drug Targets and Side Effects

    • Increasing drug dosage can engage multiple targets, leading to side effects, often unwanted.
    • Low potency drugs require higher doses, increasing the chance of 'on-target' and 'off-target' side effects.
    • 'On-target' side effects occur through the same receptor responsible for the desired effect, e.g., opioids causing constipation and respiratory depression.
    • 'Off-target' side effects arise from different mechanisms, as seen with dimenhydrinate affecting multiple receptors.

    Dimenhydrinate and Its Mechanism

    • Dimenhydrinate, commonly known as Gravol or Dramamine, is an antiemetic used for nausea.
    • Its primary component, diphenhydramine, is an H1 receptor antagonist, inhibiting histamine actions in the brain.
    • It causes drowsiness by antagonizing muscarinic acetylcholine receptors.
    • Misuse of Dramamine may lead to delirium, referred to as "Dramatizing".

    Dose-Response Curves

    • Biological response to drugs is measured using concentration-effect or dose-response curves.
    • These curves show a graded response increase as drug concentration rises (e.g., increased heart rate with epinephrine).
    • Maximum cellular activity reaches a limit, represented by the overflow when stimulus exceeds capacity.

    Efficacy and Agonism

    • Efficacy (Emax) denotes the maximal effect attributed to a drug.
    • Differentiates between full agonists, which activate receptors strongly, and partial agonists, which activate them weakly.
    • Efficacy is determined by the strength of the agonist-receptor complex and its ability to stabilize the active receptor state.

    Affinity vs. Efficacy

    • Affinity reflects a drug's tendency to bind to receptors, while efficacy measures the ability to activate the receptor post-binding.
    • High potency often correlates with high affinity, allowing significant effects at lower drug concentrations.
    • Agonists typically exhibit high efficacy, while antagonists, like naloxone, have zero efficacy but can block receptor activation.

    Potency

    • Defined by drug affinity and efficacy, referring to the dose required to yield 50% of the maximal effect (EC50 or ED50).
    • Potency quantifies drug effectiveness through varying responses on a dose-response curve.
    • A lower EC50 indicates higher potency, allowing effective response at lower concentrations.

    Receptor Reserve

    • Receptor reserve exists when available receptor sites greatly exceed cell signaling capacity.
    • Occupying a small percentage of receptors can produce maximal response.
    • Different tissues may show varied responses to the same agonist based on receptor reserve levels.

    Summary of Dose-Response Curves

    • Dose-response curves facilitate estimating Emax (maximum response) and EC50 (dose for half the maximal response).
    • They do not directly measure full agonist binding affinity due to the complex relationship between occupancy and physiological response.
    • For partial agonists, EC50 approximately reflects their affinity for receptors.

    General Characteristics of Drug Targets

    • Drug targets are mainly human proteins and biomolecules critical for disease modulation.
    • Approximately 667 human proteins and 28 other biomolecules are recognized as molecular drug targets.
    • Identifying relevant targets that influence disease progression is a significant challenge.

    Understanding Drug Binding and Activation

    • Drug "target" refers to the biochemical entity where a drug binds to initiate its effect.
    • Protein targets include receptors, enzymes, transporters, and ion channels.
    • Distinction exists between drug receptors (function in signal transduction) and broader drug targets (including non-protein entities like DNA and lipids).

    The Role of Protein Structure

    • Proteins possess tertiary structures essential for molecular binding, impacting electronic interactions with drugs.
    • Drug binding causes specific physiological responses via receptor activation.

    Agonists and Antagonists

    • Agonists activate receptors, eliciting tissue responses by binding to the active receptor conformation.
    • Antagonists bind to receptors but do not activate them, inhibiting the effects of agonists.
    • Receptor ligands encompass both agonists and antagonists.

    Binding and Activation Process

    • Binding may not always lead to activation; it merely occupies receptor sites.
    • Agonists possess high affinity for the active receptor state, promoting activation.
    • Receptor activity depends on the equilibrium between active and inactive states influenced by drug binding.

    Affinity and Efficacy

    • Affinity is the tendency of a drug to bind to its receptor; efficacy is the capability to activate the receptor post-binding.
    • High affinity drugs may have lower equilibrium constants (KA), indicating effective receptor occupation.
    • The EC50 value is used to measure the concentration of a drug that produces 50% of its maximal effect.

    Potency and Dose-response Relationships

    • Potency reflects the drug concentration required for a specified response, influenced by both affinity and efficacy.
    • Dose-response curves illustrate the relationship between drug concentration and biological effect.
    • The concept of 'spare receptors' indicates that not all receptor binding is necessary for maximum cellular response, impacting different tissues differently.

    Key Definitions

    • Binding: The occupation of a receptor by a drug molecule; may not lead to receptor activation.
    • Activation: Changes in receptor function leading to a physiological response.
    • Receptor Reserve: The phenomenon where excess receptor sites available can enhance drug potency without complete occupancy.

    Summary of Key Points

    • Drug discovery relies heavily on understanding how drugs interact with specific protein targets.
    • Distinctions between agonists and antagonists are crucial for pharmacology.
    • The interplay of binding affinity and intrinsic efficacy determines drug potency.
    • Understanding dose-response relationships and receptor dynamics is essential for effective drug development.

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    Description

    This quiz covers the concepts of drug specificity and the potential for side effects when dosages increase. It explores how the potency of a drug influences its interactions with various targets. Test your understanding of drug interactions and their implications in pharmacology.

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