Drug Antagonism and PA2 Values
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Questions and Answers

What is the mechanism of action for Avastin?

  • It inhibits VEGF by preventing its binding to the kinase receptor. (correct)
  • It enhances the signaling of the VEGF protein.
  • It binds to the ES complex of VEGF and enhances its action.
  • It acts as a competitive antagonist by binding to the same site as VEGF.

    • Which type of antagonist competes directly with the agonist for the same receptor?

  • Un-competitive antagonist
  • Competitive antagonist (correct)
  • Non-competitive antagonist
  • Desensitization antagonist

    • What is the duration of validity for Schedule 2 and 3 controlled drugs?

  • Valid for 3 months
  • Valid for 28 days (correct)
  • Valid for 12 months
  • Valid for 6 months

    • Which of the following is NOT part of the accuracy check before dispensing medication?

    <p>Patient’s medical history (D)</p> Signup and view all the answers

    What must occur when collecting a Schedule 2 or 3 drug on behalf of someone else?

    <p>Identity must be checked and noted. (C)</p> Signup and view all the answers

    What type of receptors are primarily responsible for mediating smooth muscle contraction in the guinea pig ileum?

    <p>M3 receptors (D)</p> Signup and view all the answers

    What occurs when the interfacial region is saturated with amphiphilic molecules?

    <p>Formation of micelles (B)</p> Signup and view all the answers

    What effect does atropine have on the ACh-induced response at lower concentrations?

    <p>Enhances the response (B)</p> Signup and view all the answers

    What is the critical micelle concentration (CMC)?

    <p>The concentration where no further decrease in surface tension is possible (B)</p> Signup and view all the answers

    Where is aspirin located in the micelles formed by sodium dodecyl sulfate (SDS)?

    <p>In the inner core of the micelles (A)</p> Signup and view all the answers

    What substance acts as a surfactant to reduce surface tension between molecules?

    <p>Sodium dodecyl sulfate (SDS) (D)</p> Signup and view all the answers

    Which factor affects the solubility of substances most notably?

    <p>Temperature and polarity (A)</p> Signup and view all the answers

    What is a saturated solution?

    <p>A solution that cannot dissolve any more solute under given conditions (B)</p> Signup and view all the answers

    What is the first step to take when assessing a casualty?

    <p>Ensure safety by checking for danger (D)</p> Signup and view all the answers

    What does the 'R' in DRABCs stand for?

    <p>Response (A)</p> Signup and view all the answers

    When should a rescuer start CPR?

    <p>If agonal breathing is observed (D)</p> Signup and view all the answers

    What is the recommended rate for chest compressions during adult CPR?

    <p>100-120 compressions per minute (A)</p> Signup and view all the answers

    What indicates that CPR should be stopped?

    <p>All of the above (D)</p> Signup and view all the answers

    How should surfactants orient themselves at an interface?

    <p>Polar end exposed to the aqueous environment (A)</p> Signup and view all the answers

    What type of surfactant is sodium dodecyl sulfate (SDS)?

    <p>Anionic (C)</p> Signup and view all the answers

    What is the importance of checking for circulation only if the casualty is breathing?

    <p>It prevents unnecessary delays in CPR (A)</p> Signup and view all the answers

    What is the role of atropine when acting as a competitive antagonist?

    <p>Reversibly binds to muscarinic receptors to block ACh actions (D)</p> Signup and view all the answers

    How does the dose-response curve shift in the presence of a competitive antagonist like atropine?

    <p>Shifts to the right without affecting the maximal response (D)</p> Signup and view all the answers

    What is the dose-ratio when calculating the effect of an antagonist?

    <p>EC50 with atropine / EC50 without atropine (D)</p> Signup and view all the answers

    What effect does an antagonist evoke on its own?

    <p>0% effect (B)</p> Signup and view all the answers

    What formula is used to calculate the molar concentration of a substance?

    <p>Dose (g) / Body weight (kg) x MW (g/mol) (B)</p> Signup and view all the answers

    What is the primary function of aeration in a tissue organ bath system?

    <p>Provide oxygen to enhance tissue viability (D)</p> Signup and view all the answers

    What physiological response does acetylcholine (ACh) enhance in the ileum?

    <p>Increases rate and strength of contraction (D)</p> Signup and view all the answers

    What is a major distinction between an agonist and an antagonist?

    <p>Agonists enhance biological responses while antagonists block them (A)</p> Signup and view all the answers

    What is the predicted effect of adding an additional methyl group to a surfactant according to Traube's Rule?

    <p>Decrease surface tension by 3.2 (D)</p> Signup and view all the answers

    Which of the following surfactants would likely form an insoluble monolayer due to insufficient water solubility?

    <p>Surfactants with a hydrocarbon chain longer than 12 C atoms (D)</p> Signup and view all the answers

    What is necessary for weak electrolytes to dissolve into water?

    <p>Ion dissociation and hydrogen bonding (A)</p> Signup and view all the answers

    Which type of materials can form an insoluble monolayer when injected onto a surface?

    <p>Water insoluble amphiphiles and polymeric compounds (D)</p> Signup and view all the answers

    Which of the following statements about phenobarb is true?

    <p>It is generally used for animals and produced as an oral solution (D)</p> Signup and view all the answers

    What is the primary factor that allows weak electrolytes to dissociate in water?

    <p>The high dielectric constant of water (C)</p> Signup and view all the answers

    In the context of Traube's Rule, which of the following surfactants is an exception?

    <p>Polyoxyethylated non-ionic surfactants (D)</p> Signup and view all the answers

    What effect does increasing the length of a hydrocarbon chain in surfactants have according to Traube's findings?

    <p>Increases surface activity and decreases surface tension (D)</p> Signup and view all the answers

    What effect does low-dose adrenaline have on blood pressure?

    <p>Decreases blood pressure through vasodilation (B)</p> Signup and view all the answers

    Why should non-cardio selective beta blockers be avoided in asthmatics?

    <p>They block the beta-2 adrenergic receptors needed for bronchodilation. (D)</p> Signup and view all the answers

    What defines the clearance of a drug?

    <p>The volume of plasma from which drug is removed per unit time (D)</p> Signup and view all the answers

    How is the maintenance dose of a drug calculated?

    <p>Css x Cl x t / F (A)</p> Signup and view all the answers

    Which type of antagonism involves an antagonist decreasing the overall concentration of an agonist at the active site?

    <p>Pharmacokinetic antagonism (B)</p> Signup and view all the answers

    What is the formula for calculating the half-life of a drug?

    <p>T1/2 = 0.693/ke (B)</p> Signup and view all the answers

    What occurs when high doses of isoprenaline are administered?

    <p>Increased heart rate alongside vasodilation (C)</p> Signup and view all the answers

    What role does glucagon play in physiological antagonism?

    <p>It antagonizes the action of insulin. (A)</p> Signup and view all the answers

    Flashcards

    Competitive Antagonist

    A substance that competes with an agonist for binding to the same receptor, by binding reversibly.

    Dose Ratio (DR)

    The factor by which the dose of an agonist must increase to produce the same effect in the presence of an antagonist compared to without the antagonist.

    Agonist Effect

    Produces a 100% effect (or maximal) when binding to a receptor.

    Antagonist Effect

    Produces 0% effect on its own; blocks or inhibits agonist effects.

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    Molar Concentration

    Concentration of a substance measured in moles per liter (M).

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    Aeration Importance (Tissue)

    Provides oxygen to the tissue in an organ bath system to ensure proper physiological responses.

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    Acetylcholine (ACh) effect

    Increases the rate and strength of smooth muscle contraction (in the ileum).

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    Agonist vs. Antagonist

    Agonists activate biological responses, antagonists block them.

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    Muscarinic ACh Receptor (mAChR) types involved in ACh response

    M3 receptors trigger smooth muscle contraction; M2 receptors may inhibit contractions. Atropine blocks M2, potentially enhancing the overall ACh response.

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    Effect of Atropine on ACh response

    At low concentrations, atropine can enhance the ACh response, possibly by blocking inhibitory M2 receptors. High concentrations of atropine will lessen the response.

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    Solution Definition

    A single phase with two or more components dispersed at a molecular level.

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    Solvent

    The substance in which a solute dissolves.

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    Factors affecting solubility

    Temperature and polarity affect how easily a substance dissolves.

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    Surfactant function

    Surfactants reduce surface tension, aiding in emulsification, foaming, and cleaning.

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    Amphiphilic molecule

    A molecule with both hydrophilic (water-loving) and hydrophobic (water-fearing) parts.

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    Critical Micelle Concentration (CMC)

    The concentration at which a surfactant forms micelles.

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    DRABCs

    A sequence of steps for assessing a casualty: Danger, Response, Airway, Breathing, Circulation. This helps determine the type of first aid needed. A systematic way to assess the situation and decide what actions to take.

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    Agonal Breathing

    Infrequent, gasping breaths that occur when the heart is stopped. It may look like breathing, but it's not effective and requires immediate CPR.

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    Chain of Survival

    A series of steps to increase the chance of survival after a cardiac arrest. It focuses on early recognition, intervention, and support.

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    When to Stop CPR

    Stop CPR when: Professional help takes over, the casualty recovers, you become exhausted, or another trained first aider is present.

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    Surfactant

    A molecule with both polar (hydrophilic) and non-polar (hydrophobic) regions, allowing it to act as an interface between water and oil.

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    Counterion

    A charged ion that balances the charge of a surfactant molecule, helping it stay stable in solution.

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    Interfacial Tension

    The force that exists between two different phases (like water and oil), which surfactants reduce, enabling mixing.

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    Micelle

    A spherical structure formed by surfactants in solution, where the hydrophobic ends are clustered together within the sphere, and the hydrophilic ends face outwards towards the water.

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    Traube's Rule

    A rule stating that for each additional methyl group added to a surfactant's hydrocarbon chain, the surface tension decreases by 3.2 units.

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    Surface Tension

    The force that exists at the interface between a liquid and a gas, or a liquid and a solid. It's like a thin, invisible elastic skin on the surface of the liquid.

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    Hydrophilic and Hydrophobic Properties

    Hydrophilic properties attract water; hydrophobic properties repel water. Surfactants have both, allowing them to interact with both water and oily substances.

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    Insoluble Monolayer

    A single layer of molecules that are insoluble in a liquid and form at the surface, typically with the polar head groups facing the liquid and the hydrophobic tails pointing outwards.

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    Surfactants at the Surface

    Surfactants adsorbed on the surface are in equilibrium with those in the bulk liquid. This means there's a constant exchange between the surface layer and the surrounding liquid.

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    Formation of Insoluble Monolayer

    Insoluble monolayers can be formed by carefully injecting a solution of the surfactant (dissolved in a volatile solvent) onto the surface, ensuring all molecules stay at the surface.

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    Types of Insoluble Monolayers

    Two classes of materials form insoluble monolayers: Water-insoluble amphiphiles and polymeric compounds. Both have amphiphilic properties allowing them to orientate at the surface.

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    Weak Electrolyte

    A drug that acts as a weak acid/base. It dissociates into ions in water due to water's high dielectric constant, but not completely.

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    Reflex Tachycardia

    The body's natural response to a drop in blood pressure, characterized by an increased heart rate to try and restore normal blood pressure levels.

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    Beta-2 Vasodilation

    The widening of blood vessels triggered by beta-2 adrenergic receptors, particularly in non-coronary arteries and bronchioles. This leads to a decrease in blood pressure.

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    Alpha-1 Vasoconstriction

    The narrowing of blood vessels caused by activation of alpha-1 adrenergic receptors, resulting in an increase in blood pressure.

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    Isoprenaline's Action on Blood Pressure

    Isoprenaline, at low doses, can lower blood pressure by promoting vasodilation through beta-2 receptors. However, at high doses, it can raise blood pressure by increasing heart rate and contractility via beta-1 receptors.

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    Non-Cardioselective Beta-Blockers in Asthmatics

    Non-cardioselective beta-blockers, which block both beta-1 and beta-2 receptors, should be avoided in asthmatics because they can constrict the airways, making breathing difficult.

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    Clearance (Cl)

    The rate at which a drug is eliminated from the body, measured as the volume of plasma cleared of the drug per unit time. Cl = Dose/AUC.

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    Volume of Distribution (Vd)

    Indicates how widely a drug distributes throughout the body tissues, calculated as the total volume of fluid in which the drug appears to be dissolved. Vd = Dose/Co.

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    Elimination Rate Constant (Ke)

    The rate at which a drug is removed from the body. Ke = Cl/Vd.

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    Antagonist types

    Different ways antagonists block agonist action: competitive, non-competitive, un-competitive, and desensitization.

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    Non-Competitive Antagonism

    Antagonist binds to a different site on the target, altering its shape and preventing agonist binding.

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    Un-Competitive Antagonism

    Antagonist binds to the agonist-receptor complex (ES complex), preventing further action.

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    Desensitization

    The body's natural response to a stimulus by becoming less sensitive over time.

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    Study Notes

    Drug Antagonism

    • Four types of drug antagonism
      • Chemical antagonism: interaction in solution affects drug availability
      • Competitive antagonism: competition for same receptor site
      • Physiological antagonism: opposing physiological effects through different pathways
      • Non-competitive antagonism: inhibits response without direct competition for agonist binding site

    PA2 Value

    • Represents agonist potency
    • Value that requires doubling the concentration of Ach (agonist) to get the same response as Atropine (antagonist)
    • Higher PA2 value (less needed to block agonist) = Higher potency
    • (the concentration of agonist at EC50 doubles)
    • pA2 value indicates the concentration of antagonist needed to reduce agonist's effect by half
    • Formula: PA2= - log[A], where [A] is the concentration of antagonist

    Example of PA2 Calculation

    • Drug X is an antagonist, and 2 x 10-6 M of Drug X doubles the effective concentration of an agonist needed to produce a response (from 5 μM to 10 μM)
    • Using the formula, PA2 = - log(2 x 10-6) = 5.7

    Agonist Potency

    • Depends on affinity and efficacy.
      • Affinity: strength of drug binding to receptor, influences receptor occupancy by the drug.
      • Efficacy: ability of a drug to produce maximum biological response once bound to its receptor.

    Drug Affinity

    • Determined by specific interactions between drug and target receptor
    • Influences likelihood and strength of drug binding.
    • Equilibrium constant (KA): affinity of agonist for receptor; smaller KA = higher affinity.
    • Equilibrium dissociation constant (KD): tendency of agonist-receptor complex to dissociate.

    Drug Efficacy

    • Receptor activation: efficiency with which a drug activates its target receptor
    • Intrinsic activity: ability of drug-receptor complex to activate cellular processes; high intrinsic activity = more efficacious responses .
    • Effector systems: influences downstream pathways.
    • Receptor reserve: drug may be considered efficacious even if not all receptors are occupied

    Competitive Antagonism

    • Agonist and antagonist compete for same binding site on receptor.
    • Both bind reversibly
    • Reaction depends on two equilibrium constants (agonist-KA & antagonist- KAnt)
    • If KAnt less than KA, antagonist has greater affinity for receptor, requiring increased agonist concentration to overcome antagonism.

    Non-Surmountable Antagonism

    • Antagonist cannot be overcome by increasing agonist concentration.
    • Has persistent effect.
    • Not easily reversed by higher agonist concentration.

    Non-Competitive Antagonism

    • Antagonist binds to a different site than the agonist.
    • Reduces the number of available receptors for agonist (affecting overall response)

    Irreversible Antagonism

    • Antagonist binds irreversibly to either agonist or non-agonist binding sites.
    • Reduces the number of available receptors.
    • Reduces the slope and overall response.

    Does Atropine act as a competitive or non-competitive agonist?

    • Competitive Antagonist:
      • Competes with ACh for binding to muscarinic receptors
      • Produces an identical slope that shifts to the right without altering maximal response (efficacy)
      • Bind reversibly.

    Dose Ratio

    • Dose-ratio: factor by which the dose of agonist must be increased to produce the same effect when antagonist is present

    Full Agonist Effect

    • A full agonist evokes 100% effect.
    • Antagonists typically evoke 0% effect on their own

    Molar Concentration Formula

    • Conc(M) = Dose (g) / Body weight (kg) x MW (g/mol)

    Acetylcholine (ACh) Action

    • Increases rate and strength of contraction in ileal smooth muscle.

    Agonist vs Antagonist

    • Agonist: activate or enhance a biological response, mimic endogenous substances.
    • Antagonist: block or inhibit a biological response.

    Potential Receptors for ACh response

    • Muscarinic Acetylcholine Receptors (mAChRs)
      • M3 receptors mediate smooth muscle contraction
      • M2 receptors may mediate inhibition and their blockade by atropine could enhance overall response
    • Cholinergic Neurons: Interactions with pre- and post-synaptic receptors might contribute to observed effects.

    Solution

    • Consists of a single phase of two or more components, where components are dispersed at a molecular level.
    • Solvent: the substance in which the solute dissolves.

    Solubility Factors of Aspirin

    • Temperature and polarity greatly affect solubility.

    SDS (Sodium Dodecyl Sulfate)

    • Surfactant that reduces surface tension between molecules.
    • Functions in emulsification, foaming, and cleaning.
    • Possesses both hydrophilic and hydrophobic groups (amphiphilic)

    Micelles

    • Form when interfacial region of amphiphilic molecules is saturated.
    • Further reduction in surface tension is not possible
    • Critical Micelle Concentration (CMC): concentration where surfactant forms micelles.

    Aspirin Location in SDS Micelles

    • Aspirin's aromatic ring is hydrophobic; located in the inner core of SDS micelles.

    Traube's Rule

    • Depends on the balance between hydrophilic and hydrophobic properties.
    • Homologous series of surfactants: Increased length of hydrocarbon chain = increased surface activity = decreased surface tension.
    • Every additional methyl = decrease in surface tension by 3.2

    Insoluble Monolayers

    • Surfactants exist in equilibrium with surfactant molecules in the bulk liquid.
    • If the surfactant has a long alkyl chain, it has insufficient water solubility and forms insoluble monolayers at the surface.
    • Heads down, tails out of water.

    Weak Electrolytes

    • Drugs that can act as weak acids or bases (often in salt form)
    • Examples: Phenobarbital

    DRABC (Casualty Assessment)

    • Danger: Don't put yourself at risk
    • Response: Check for any response (e.g., shouting)
    • Airway: Open airway (tilt head back, lift chin)
    • Breathing: Check for breathing (10 seconds)
    • Circulation: Check for bleeding, but only if breathing is normal
    • Resuscitation procedures (CPR)

    Chains of Survival

    • Recognize cardiac arrest
    • Call emergency services
    • Early basic life support
    • Early defibrillation
    • Early advanced life support

    Surfactant (Amphiphile)

    • Distinctive polar and non-polar regions (hydrophilic and hydrophobic)
    • Polar regions can be: anionic, cationic, zwitterionic, or non-ionic.

    Dispensed Drug Checks

    • Accuracy: Labels, correct medicine, Patient information etc
    • Legal: prescription details, date, CD requirements etc.
    • Clinical checks: drug suitability for condition, any contraindications etc.

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    Description

    This quiz covers the four types of drug antagonism, including chemical, competitive, physiological, and non-competitive antagonism. It also explores the PA2 value, its significance in measuring agonist potency, and how to calculate it using specific examples.

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