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Disease & Defense > LEC 25 Mechanisms of Drug Action > Flashcards

LEC 25 Mechanisms of Drug Action Flashcards

1
Q

Why are drugs with weaker binding forces more selective?

A

The weaker binding forces means that the drug must be a very close fit to the receptor ie it is more selective toward the receptors it will bind

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2
Q

What are the specific binding characteristics between a drug and a receptor?

A
  • Sensitivity
  • Selectivity
  • Specificity
  • Saturability
  • Reversibility
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3
Q

What is the Hill equation?

A
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4
Q

The graphical representation of the relationships demonstrated by Hill equation is called what kind of curve?

A

Graded Dose-Response Curve

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5
Q

Drugs that produce an effect are called what?

A

Agonists

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6
Q

What two parameters can be determined from a dose-response curve?

A
  1. Potency (ED50)
  2. Maximal Effect of a Drug (Emax)
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7
Q

What is potency?

A

ED50 - the amount of drug that produces half of the maximal effect

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8
Q

What is efficacy?

A

Emax - the maximal effect produced by a drug

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9
Q

In practice, the dose [D] in a graded dose-response curve is usually plotted on a log scale. This produces what kind of curve?

Why is this better?

A

Sigmoidal

Makes Emax easier to determine

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10
Q

Differentiate between Kd and ED50.

A
  • Kd is associated with the receptors. It is a measure of affinity for the drug. It is when 1/2 of the receptors are activated (which is usually half of Emax).
  • ED50 is a measure of potency of the drug or how well the drug activates a receptor to produce a response

Both are the x axis value at 50% of Emax; same value, but diff meaning

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11
Q

When comparing 2 drugs (A & B), drug A has a lower ED50 than drug B. What does this tell us about A’s potency relative to B

A

Drug A is MORE POTENT than Drug B

Lower ED50 means more potent

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12
Q

What is a partial agonist?

A

a drug that binds the receptor and produces a different conformational change that is NOT as efficacious at activating the signalling pathway as a full agonist (“partial response”)

a drug that produces an effect but its Emax is less than full agonist

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13
Q

What kind of data is plotted on quantal dose-response curves?

A
  • plot quantal responses in a population
  • “yes or no outcomes”
  • Percentage of population showing some defined effect
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14
Q

How do we use a quantal dose effect curve to compare potency for both therapeutic and toxic/lethal effect of a drug?

A
  • Both therapeutic and toxic/lethal responses are plotted on the same graph using different curves
  • Compare the ED50 and TD50/LD50
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15
Q

How is the therapeutic index (TI) calculated?

A

=LD50/ED50

ideally, this should be a large number and will always be greater than 1

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16
Q

What is the problem with using TI=LD50/ED50 from the quantal dose-response curve?

A
  • Assumes the curves are parallel which may not be true
  • may be overlap on the curves meaning that a therapeutic dose for some is a toxic dose for others
17
Q

What are the characteristics of a full agonist?

A
  • High affinity
  • produces full efficacy
18
Q

What are the characteristics of an antagonist?

A
  • High affinity
  • NO EFFICACY
  • Blocks the effect of endogenous substances or exogenously administered drugs
19
Q

What are the characteristics of a partial agonist?

A
  • High affinity
  • Less efficacy than full agonist
  • can block the effects of full agonist
20
Q

What are the characteristics of an inverse agonist?

A
  • produces the opposite effect of the agonist
  • may or may not have equal efficacy to agonist
  • bind receptors that are constantly activated and turn them off so the basal activity of that receptor type is reduced
21
Q

What is pharmacological antagonism?

A
  • Two drugs that act on the same receptor site: (an agonist and an antagonist)
  • Can be competitive or non-competitive

Ex: Fentanyl and Naloxone

22
Q

What occurs in competitive antagonism?

A
  • POTENCY DECREASES
  • Efficacy stays the same
  • Shifts ED50 to the right
  • More drug needed to produce an effect with the antagonist present
23
Q

What occurs in non-competitive antagonism?

A
  • EFFICACY DECREASES
  • No shift in ED50 - Potency stays the same
  • Effect CANNOT be overcome by increasing the dose
  • antagonist binding is IRREVERSIBLE
24
Q

What is functional or physiological antagonism?

A

Two agonists binding to different receptors with opposing effects

Estrogen/Testosterone & Histamine/Epinephrine

25
Q

What is chemical antagonism?

A
  • No pharmacological receptors involved
  • A chemical rxn
  • Results in a new compound or an inactive complex

Ex: antacids neutralize stomach acid

Disease & Defense (37 decks)

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