Drug binding/affinity malark

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2 examples of stereoisomers and their effects on drug binding
- Acetyl-beta-methylcholine: (cholinergic agonist) inactive isomer has no affinity - simple right shift due to reduction in concentration of active isomer
- Isoprenaline: (beta agonist) inactive isomer is an antagonist - line becomes straight as concs of both increase
EC50
- Concentration of drug that produces 50% of the maximal response
- Gives potency
Partial agonist eg

Butyryl choline (55% of ACh)
Significance of dissociation constant

equal to the drug concentration that produces 50% occupancy of the receptors
Describe Scatchard plot
- x axis: B
- y axis: B/[D]
- slope: -K1
- x intercept: Bmax
Determination of affinity for a competitive agonist
- Use two concentrations
- Dose ratio [D1]/[D2] = 1 + [A]K2
Binding of drug D in the presence of A which binds to the same receptors

alpha = ([D]K1)/(1 + [D]K1 + [A]K2)
Finding affinity for a competitive ligand in a radioligand binding experiment
- plot x axis: log[unlabelled drug]
- y axis: %bound radioligand
- find IC50 from graph
- Ku = (1+ [L]KL) / IC50
- where Ku = affinity constant of unlabelled drug
- KL = affinity constant of labelled drug
IC50

The concentration of an antagonist that inhibits 50% of the specific binding of the agonist
Example to demonstrate receptor reserve
how do you do it
- Benzilylcholine mustard - irreversibly alkylates muscarinic receptor (time dependent)
- Find dose ratio at maximum ressponse - can estimate % of receptors that are spare
Hill plot
- x axis: log[D]
- y axis: log {B/(Bmax -B)}
- slope = nH
- nH = 1: no cooperativity etc
What is Therapeutic Index?
- Toxic dose / Therapeutic dose
- LD50 / ED50 (lethal dose/effective dose)

Author

mfawcett

185137

Card Set

Drug binding/affinity malark

Description

moda

Updated

2012-12-31T10:10:33Z

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