Equilibrium constant

on 14.1.09 with 0 comments



Keq = [DR]/[D][R]

= drug-receptor association constant, binding constant, or affinity constant.

Keq tells how strongly the drug binds to a receptor.


[R]total = sum of both bound and unbound receptors = [DR] + [R]

([DR] and [R] can both change, but [R]total stays the same)


Now we can do some manipulation… how does [DR] change as we add more drug?

This will produce the dose-response curve (shown on page 2 of handout)

First, write equilibrium constant as: [DR] = Keq [D][R]

Then define [R] as: [R] = [R]total – [DR]

…and solve for [DR]


what you get is: [DR]/[R]total = Keq[D]/(1 + Keq[D])


…notice that [DR]/[R]total is the fraction of the total number of binding sites with drug bound to it. This is what we want because its related to the amount of free drug that we have.

Category: Pharmacology Notes

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