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Pharmocolgy > P1: How do drugs work? > Flashcards

P1: How do drugs work? Flashcards

1
Q

What is a drug?

A

A substance that affects the body and elicits a change in physiology

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2
Q

What is the receptor theory for drug action?

A
  • Drugs act by binding to targets and inducing a response

- Drugs do not work until they bind to their receptors

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3
Q

Define agonist

A
  • Agents that elicit a positive response

- Eg. mimic NTs

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4
Q

Define antagonist

A
  • Agents that act as inhibitors

- Prevent activity of endogenous hormones, enzymes and neurones

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5
Q

Define partial agonist

A
  • Agents that elicit a positive response, but not to the complete extent possible
  • Used for controlling
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6
Q

Define the law of mass action

A

The rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants

(ROR = Conc of reactants)

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7
Q

What is Kd? (2)

A

This is the dissociation constant, which is the concentration of a drug which, at equilibrium, occupies 50% of the available receptors.

It measures the likelihood that a Drug and Receptor will dissociate, higher Kd = lower binding.

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8
Q

What is Ka?

A

Affinity constant
indicates the readiness of the drug binding to a receptor
The higher the affinity, stronger the binding

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9
Q

Higher Kd means _____ affinity

A

Lower

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10
Q

Higher Ka means _____ affinity

A

Higher

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11
Q

Define potency

A

Dose of a drug necessary to have an effect

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12
Q

What does a low dosage say about the potency of a drug

A

Lower dosage = Higher potency

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13
Q

Define Efficacy

A

The effectiveness of a drug

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14
Q

What is Emax

A

Maximum effect achievable

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15
Q

What are the 3 major types of receptor antagonism?

A
  • Reversible competitive
  • Irreversible competitive
  • Allosteric
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16
Q

Describe reversible competitive antagonisms affect on the Emax and log,dose(agonist) response curve

A

Emax not depressed

Parallel shift to the right in the dose response curve (EC50 rises)

17
Q

Describe the mechanism of irreversible competitive antagonism

A

Binds covalently to the receptor active sites, therefore:

  • decrease total number of available receptors
  • decreases maximum response achievable (Emax)
18
Q

Where do allosteric antagonists bind?

A

Binds to a separate site on the receptor from the ligand

19
Q

How do allosteric antagonists work?

A
  • Alters conformation of receptor

- Limiting agonist binding

20
Q

What does pA2 rank?

A

Antagonist potency

21
Q

What is the EC50

A

This is the dose of a drug needed for a half maximal response, it is a measure of potency.

22
Q

What can a Scatchard Plot be used for with drugs

A

These can detect drugs that can have 2 or more binding sites with different affinities

23
Q

What is the therapeutic window

A

This is the gap in doses between therapeutic and toxic effects

24
Q

What is an inverse agonist and name an example

A

Elicits the opposite response to the endogenous ligand e.g. naloxone for heroin overdose

25
Q

How is the dissociation constant (Kd) related to the affinity constant (Ka)

A

1/Kd = Ka

Affinity constant is inversely proportional to the dissociation constant

26
Q

What is the shape of a dose response curve with Dose(agonist) on the x-axis and Response on the y-axis

A

Rectangular hyperbola

27
Q

What is the shape of a dose response curve with Log[Dose(agonist)] on the x-axis and Response on the y-axis

A

Sigmoidal curve

28
Q

Give an example of a reversible, competitive antagonist

A

Tolazoline on alpha-adrenceptors

29
Q

How does irreversible competitive antagonism affect a Log Dose [Agonist]/Response curve

A

Non parallel shift and depressed Emax

Occasionally parallel shifts and no depression of the maximum - spare receptors

30
Q

Give an example of an irreversible competitive antagonist

A

Phenoxybenzamine on alpha-adrenoceptors

31
Q

How does allosteric antagonism affect a Log[Dose]/Response

A

No change in EC50, Reduced Emax

32
Q

Gives an example of a reversible and irreversible allosteric antagonist

A

Reversible - Memantine on NMDA receptors

Irreversible - aspirin on cyclo-oxygenase 1

33
Q

What kind of drug are schild plots valid for

A

competitive antagonists

34
Q

What is the x - intercept in a schild plot

A

an estimate of the antagonist equilibrium dissociation constant, pA2.

Pharmocolgy (22 decks)

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