Drug affinity Flashcards
What is receptor occupation governed by?
Affinity
What is activation governed by?
Efficacy
By definition what efficacy does an antagonist have?
0
How can the total number of binding sites be identified?
Scatchard plot
What is KD?
KD = conc. required for 50% occupancy
Constant that defines the affinity of a drug for a receptor
Higher the KD = higher dissociation = lower affinity
What is the forwards rate?
Forward rate = k+1 [A][R]
What is the backwards rate?
Backwards rate = k-1 [AR]
Write the equation at equillibrium
k+1[Aeq][Req] = k-1 [AReq]
Write equation for KD at equillibrium
KD = k-1/k+1 = [Aeq][Req]/[AReq]
What happens when drug affinity is increased?
KD reduced
Increased occupancy at low concentrations
What is the occupancy of a preparation if all receptors are filled?
1 or 100%
Could be written as percentage saturation
How is occupancy determined?
Occupancy = N of receptors occupied / Total N receptors
Why is measuring response not a good way of determining the effectiveness of a drug?
Some drugs produce the same responses at very low concentrations/ occupancy because they have a high affinity and efficacy
What is 100% saturation known as
Bmax
Concentration of agonist at 100% saturation
What happens when an agonist is bound to a receptor?
When agonist bound stabilises protein structure which favours signalling
