Mechanisms of drug action

Question 1

What are the types of drug antagonism

Answer 1

Receptor blockade
Physiological antagonism
Chemical antagonism
Pharmacokinetic antagonism

Question 2

What are the types of receptor blockade

Answer 2

Competitive or irreversible

Question 3

Describe physiological antagonism and give an example

Answer 3

Different receptors cause opposite effects on the same tissue e.g. NA and histamine on blood pressure

Question 4

Describe chemical antagonism and give an example

Answer 4

Interaction in solution

Dimercaprol and heavy metal complexes

Question 5

Describe pharmacokinetic antagonism and give an example

Answer 5

Antagonist decreases the concentration of active drug at the site of action
Barbiturates

Question 6

What is drug tolerance + example

Answer 6

Gradual decrease in responsiveness to a drug with repeated administration
e.g. benzodiazepines

Question 7

How do pharmacokinetic factors contribute to drug tolerance + example

Answer 7

Decreases as rate of metabolism increases

Barbiturates and alcohol

Question 8

How does a loss of receptors contribute to drug tolerance + example

Answer 8

Due to membrane endocytosis
Receptor down regulation

Beta-adrenoceptors

Question 9

What are the causes of an increase in drug tolerance

Answer 9

Pharmacokinetic factors
Loss of receptors
Change in receptors 
Exhaustion of mediator stores
Physiological adaption

Question 10

How does a change of receptors contribute to drug tolerance + example

Answer 10

Receptor desensitisation leading to a conformation change

nAChR at NMJs

Question 11

Give an example of a drug whereby the tolerance is affected by exhaustion or mediator stores

Answer 11

Amphetamine

Question 12

How does physiological adaption contribute to drug tolerance

Answer 12

Homeostatic responses

Tolerance to drug side effects

Question 13

What are the 4 types of receptor families based on

Answer 13

Molecular structure

Signal transduction system

Question 14

Describe the type 1 receptor family + example

Answer 14

Ion channel-linked receptors
Fast responses (ms)
nAChR, GABAa

Question 15

Describe the type 2 receptor family + example

Answer 15

G-protein coupled receptors
Slower (s)
Beta-adrenoreceptors in the heart

Question 16

Describe the type 3 receptor family + example

Answer 16

Kinase-linked type
Slow (min)
Insulin/growth factors

Question 17

Describe the type 4 receptor family + example

Answer 17

Intracellular steroid type receptors
Slow (hours)
Steroids/thyroid hormones
Regulate DNA transcription

Question 18

Describe use-dependency

Answer 18

An increase in the activity of the tissue will cause the drug to act more quickly