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DEN 2026 - Pharmacology > Agonists and Antagonists > Flashcards

Agonists and Antagonists Flashcards

1
Q

What are the 3 main molecular targets for drug action?

A
  1. Proteins
  2. Nucleic acids
  3. Miscellaneous targets e.g. metal ions and GIT contents
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2
Q

What is a receptor?

A

Protein target with which a naturally occurring chemical mediator binds specifically to initiate a cellular response

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3
Q

What are the two classes of chemical mediators?

A
  1. Cell surface receptors

2. Intracellular receptors

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4
Q

What is the function of cell surface receptors?

A

Act as a receptor for molecules too large or hydrophilic to cross the cell membrane

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5
Q

What is the function of intracellular receptors?

A

Act as receptors for molecules which are small enough and hydrophobic so can pass through cell membrane

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6
Q

What happens when a chemical mediator on binding with receptor?

A

Shape change which stabilises the active form of a receptor so enhances interaction with signal transduction mechanism

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7
Q

What are the 2 stages of drug action on receptors?

A
  1. Binding

2. Activation

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8
Q

What is the function of an agonist?

A

Mimic the action of the chemical mediator, cause a shape change so causes a response in a cell or tissue

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9
Q

What is the function of an antagonist?

A

Bind to the receptor but does not cause a shape change so there is no response in a cell or tissue

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10
Q

What 5 factors affect the size of a response to a receptor agonist?

A
  1. Concentration of drug molecule
  2. Affinity
  3. Intrinsic efficacy
  4. Natural of signal transduction mechanism
  5. Total numbers of receptors present
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11
Q

What 4 things can influence the concentration of a drug molecule?

A
  1. Dose given
  2. Route of administration
  3. Distribution
  4. Rate of elimination
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12
Q

What is the affinity of a drug?

A

Tendency of a drug to bind to a receptor (strength of attraction)

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13
Q

What is the intrinsic efficacy of a drug?

A

Ability of a drug to activate a shape change in receptor so cause response

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14
Q

What 2 factors affect the proportion of total receptors available occupied?

A
  1. [Agonist]

2. Affinity

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15
Q

How do most agonists bind?

A

Reversibly

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16
Q

What is the Occupancy Equation?

A

[Agonist] / [Agonist] + Ka

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17
Q

What does Ka stand for?

A

It is the drugs equilibrium constant

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18
Q

How is the Ka value of a drug found?

A

It is equal to the concentration of agonist when half the receptors are occupied

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19
Q

What does Ka measure?

A

Strength of bonds formed between agonists and receptors

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20
Q

What happens if a drug has a high affinity to a receptor?

A

Strong bonds form so small [agonist] sufficient to achieve high occupancy

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21
Q

Ka is a theoretical measure. What is the practical measure and how does it work?

A

EC50 which measures drug potency downstream of a receptor

22
Q

What is a full agonist?

A

Drug which causes maximum response in receptors i.e. activates shape change in all receptors

23
Q

What is a partial agonist?

A

Drug which produces a smaller than maximum response even at high concentrations

24
Q

What is the efficacy of a full agonist?

A

1

25
Q

What 4 types of coupling can affect the extent of amplification of the initial signal and size of a response?

A
  1. Chemical gating of ion channels
  2. Activation of G-proteins
  3. Direct activations of enzymes
  4. Regulation of gene transcription
26
Q

What are antagonist drugs?

A

Any drug which reduces the response to another drug

27
Q

What are 5 types of antagonist?

A
  1. Competitive
  2. Non-competitive
  3. Physiological
  4. Pharmacokinetic
  5. Chemical
28
Q

What is a competative antagonist?

A

Drugs which compete with naturally occurring chemical mediators or agonists for a binding site on receptor without initiating a cellular response

29
Q

What is the intrinsic efficacy of competative antagonists?

A

0

30
Q

What is the competitive antagonist for B1 adrenoreceptor?

A

Atenolol

31
Q

How does atenolol work?

A

Competes with agonist for binding site but cannot cause a shape change so the muscle does not contract

32
Q

What is a clinical use of atenolol?

A

Prevent angina as ability of adrenaline and noradrenaline to increase cardiac work is blunted

33
Q

What are the 2 classifications of competitive antagonists?

A
  1. Reversible

2. Non-reversible

34
Q

What is the only way to influence reversible antagonists?

A

Increase concentration of agonists

35
Q

What is the effect of a competitive reversible antagonist on the agonist log concentration response graph?

A

No reduction in maximum response but a greater concentration is needed to produce maximum response

36
Q

Why do some antagonists bond irreversibly?

A

They form covalent bonds

37
Q

What is the only way to overcome irreversible antagonists?

A

Create new receptors

38
Q

What is an example of an irreversible antagonist drug?

A

Clopidogrel

39
Q

What is the function of clopidogrel?

A

Anti-platelet drug to inhibit thrombus formation

40
Q

What is the effect of a competitive irreversible antagonist on the agonist log concentration response graph?

A

Progressive reduction in maximum response to agonist without a shift in concentration

41
Q

What is a non competitive antagonist?

A

An antagonist which affects action of agonist at some point in the chain leading to a response but does not compete for the same binding receptor as the agonist

42
Q

Give 2 examples of how non competitive antagonists can work

A
  1. Binding to an allosteric site to cause conformational change on agonist receptor
  2. Interference with a component of the signal transduction pathway
43
Q

What is a physiological antagonist?

A

An antagonist with an opposite affect to an agonist but achieves the result by acting on separate cells i.e. two systems are involved

44
Q

What is an example of a physiological antagonist?

A

Parasympathetic nervous system releasing acetylcholine in nerves supplying heart to counter sympathetic response

45
Q

What is a pharmacokinetic antagonist?

A

A drug concentration can be decreased if another drug interferes with its ADME

46
Q

What are 2 examples of chemical antagonists?

A
  1. Heparin

2. Protamine sulphate

47
Q

How are receptors initially divided?

A

Receptor families

48
Q

How are receptor families divided?

A

Family members

49
Q

What are receptor families based on?

A

Which mediators a receptor responds to

50
Q

What 3 things are family members based on?

A
  1. Potency of endogenous mediators at receptors for that mediator in different tissues
  2. Selective stimulation by agonist drugs
  3. Selective blockade by competitive antagonist drugs

DEN 2026 - Pharmacology (22 decks)

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