LHD - Types of Agonist

Question 1

How do you determine the pA2 value for an antagonist on a Gaddis schild plot?

Answer 1

X-intercept: -pA2

Question 2

How do you distinguish between competitive and non-competitive antagonism?

Answer 2

Use pAx

• The negative logarithm of the concentration that gives a dose ratio of x

Log(x-1) = pA2 - pAx

Question 3

What does a substantial deviation away from the expected pAx equation value indicate?

Answer 3

The interaction between the antagonist and the agonist at the receptor is not competitive

Question 4

What are the main assumptions of the occupancy theory? (2)

Answer 4

2. All agonists for a given receptor can produce the same maximum response
3. The maximum response occurs when all the receptors are occupied

Question 5

What are partial agonists?

Answer 5

Drugs that act on receptors and only produce a weak response

• Act as competitive antagonist of the full agonist

Question 6

What is a problem with the occupancy theory?

Answer 6

Not all agonists are capable of producing a full response

Question 7

Can a maximum response be obtained when not all the receptors are occupied?

Answer 7

Yes, (problem with assumption 6)

Question 8

What are SPARE RECEPTORS?

Answer 8

An agonist with high efficacy may only need to bind to a small fraction of receptors to produce a maximum response

Question 9

What modifications are made to the occupation theory to account for partial agonists? (2)

Answer 9

1. The effect will depend on the AFFINITY of the drug for the receptor
2. The effect will depend on the ability of the drug to induce a conformational change in the receptor

Question 10

What is an inverse agonist?

Answer 10

An inverse agonist produces an effect opposite to that of an agonist