Dose Response Relationships

Question 1

Define bioassay

Answer 1

The quantitative measurement of drug efffect in intact biological systems

Question 2

Law of mass action - AGONIST

Answer 2

Question 3

What are isolated tissues

Answer 3

Whole organs placed in heated chambers, incubated with physiological salt solutions, kept at physiological pH and perfused with O2 such that they behaved as in the intact organism

* enabled quantitative measurements to be made

Question 4

What do dose-response curves measure

Answer 4

The relation between the conc of drug and some physiological response (as opposed to binding)

• Rise in BP
• Contraction/relaxation of SM

Question 5

Contraction traces following addition of an agonist

Answer 5

Question 6

Dose response curve plotted from contraction traces

Answer 6

Question 7

What is the EC₅₀

Answer 7

Concentration that produces half of the maximal response

Question 8

Name the 2 measurements dose-response curves can estimate

Answer 8

POTENCY

• Conc needed to produce 50% response
• Half-max EC₅₀ (conc) or ED₅₀ (dose)

EFFICACY

• Max response (E_max)
• State at which signalling is maximum - more drug will give no addition response

Question 9

Define ED₅₀

What is is related to (in terms of the receptor)

What effect does a lower ED₅₀ have on the potency

Answer 9

• Dose of drug that produces 50% of its own maximum effect
• Related to affinity of drug for receptor
• The lower the ED₅₀, the greater the potency of the drug

Question 10

Define a graded dose-response relationship

Answer 10

• Measured in a single biological unit
• Continuous scale (dose -> effect)
• Relates dose to intensity of effect

Question 11

Define a quantal dose-response relationship

Answer 11

• Population studies
• All or none pharmacological effect
• Relates dose to frequency of effect
• Variation among individuals

Question 12

Which drug is more potent

Which drug has greater efficacy (max response)

Answer 12

Drug A will give half a maximal response at lower conc than drug B but both will eventually produce the same maximal response

=> Drug A and drug B have the same EFFICACY but POTENCY differs

Drug A is more potent than drug B because it has a lower EC₅₀ than drug B

Question 13

Effect of a lower EC₅₀ on potency

What does E_max inidicate

Answer 13

The lower the EC_50, the higher the potency

The higher the E_max, the greater the effect (efficacy)

• Drug A is more potent than drug B but both show the same efficacy
• Drug C has lower potency and efficacy

Question 14

Potency vs efficacy on a graph

Answer 14

Question 15

Comparison of potency of ibuprofen and aspirin

Answer 15

Ibuprofen is more potent than aspirin

Question 16

Comparison of the potency and efficacy of morphine and aspirin

Answer 16

Morphine is more potent and has greater efficacy