Pharmacodynamic: Two State Receptor Model

Question 1

Explain the concept of the 2 state receptor model?

Answer 1

That the receptor exists in two forms: the activated form and the inactivated form

That when in the absence of a ligand the receptor is non functional but when in the presence of one it is functional

But there are receptors that have little basal acitivity in the absence of a drug

Question 2

What are the 2 states receptor exists in?

Answer 2

Activated

Inactivated

Question 3

An agonists has a higher affinity for the receptor in the activated state therefore……

Answer 3

The equlibrium shifts to the activated state of the receptor

Question 4

An antagonists has an equal affinity for the activated and inactivated state of the receptor therefore…..

Answer 4

There is no change in the equilibrium, it remains constant

Question 5

An inverse agonist has a higher affinity for the receptor in the inactivated state therefore….

Answer 5

The is an equilibrium shift to the inactivated state of the receptor

Question 6

Which inverse agonist has an effect on the beta -adrenergic receptors?

Answer 6

Propanolol

Question 7

Which inverse agonost has an effect on the histaminergic receptors and is used to treat Allergic Rhinitis?

Answer 7

Cetirizine

Question 8

Which inverse agonist acts to block the production of HCl inorder to treat patients with heart burn?

Answer 8

Ranitidine

Question 9

What is potency depended on ?

Answer 9

It is depended on the affinity of the drug to the receptor and the success of the binding to the receptor

Question 10

Explain the concept of spare receptors?

Answer 10

Increased amounts of receptors that are not bound, increases the sensitivity of the receptors to the drug therefore more binding and therefore increased cellular response

Question 11

Why is it that the maximal response of the cell to the drug is inversly proportional to the fractional occupancy of the receptors?

Answer 11

If more receptor are bound therefore less ligand are there to actually be metabolised so that they can be active. So less drug unbounded, increased activity.

Question 12

Explain the concept of receptor trafficking?

Answer 12

It is the internalisation of the receptors, therefore decreasing sensitivity of the receptors to the drug and this results in less activity of the drug in the body

Question 13

How is drug trafficking related to drug resistance?

Answer 13

If there are less receptors for the drug to bind there is less activity therefore action of the drug is irrelevant

Question 14

There are two types of receptor internalisation, what are they?

Answer 14

Tachyphylaxis

Tolerance

Question 15

What is tachyphylaxis?

Answer 15

It is the rapid desensitisation of the receptor to the drug thus resulting in no effect of the drug in the body

Question 16

What is tolerance?

Answer 16

It is the slow and gradual decrease in the sensitivity of the receptor to the drug

Question 17

How can one counteract tolerance?

Answer 17

By increasing the dose of the drug

Question 18

What is refractiveness?

Answer 18

It is a condtion in which the patient is unresponsive to the drug treatment

Question 19

Refractiveness is depended on……

Answer 19

• Internalisation of the receptors
• Exhaustion of mediators such as enzymes or transportes
• Increased metabolic degradation of the drug