Drug binding/affinity malark

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  1. 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
  2. EC50
    • Concentration of drug that produces 50% of the maximal response
    • Gives potency
  3. Partial agonist eg
    Butyryl choline (55% of ACh)
  4. Significance of dissociation constant
    equal to the drug concentration that produces 50% occupancy of the receptors
  5. Describe Scatchard plot
    • x axis: B
    • y axis: B/[D]
    • slope: -K1
    • x intercept: Bmax
  6. Determination of affinity for a competitive agonist
    • Use two concentrations
    • Dose ratio [D1]/[D2] = 1 + [A]K2
  7. Binding of drug D in the presence of A which binds to the same receptors
    alpha = ([D]K1)/(1 + [D]K1 + [A]K2)
  8. 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
  9. IC50
    The concentration of an antagonist that inhibits 50% of the specific binding of the agonist
  10. 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
  11. Hill plot
    • x axis: log[D]
    • y axis: log {B/(Bmax -B)}
    • slope = nH
    • nH = 1: no cooperativity etc
  12. What is Therapeutic Index?
    • Toxic dose / Therapeutic dose
    • LD50 / ED50 (lethal dose/effective dose)
Card Set:
Drug binding/affinity malark
2012-12-31 10:10:33

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