Medicinal Chemistry Applet

log(dose)-response relationships

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Introduction

Dose-response plots (see dose-response applet) (eq. 1) are useful for evaluating the relative ability of agonists, both partial and full, to elicit a response.  These plots are not very helpful for readily identifying difference in the affinity of a drug for its receptor (KD).  More effective are log(dose)-response plots (or log[D]-response).  The log(dose)-response relationship works to highlight the region of highest interest, where the percentage of response is increasing at the highest rate.  Naturally, in a log(dose)-response plot, the response will reach 50% at when log[D] = log[ED50] since the x-axis is logarithmic.  Sometimes, drugs will be reported with their log[ED50] values instead of simple ED50 values.

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Applet

This applet plots % response vs log[D] data for up to three compounds.  For each compound, the ED50 and e (efficacy or intrinsic activity) must be specified.  The units of EC50 and [D] are concentration, but log[D] is unitless.  Efficacy/intrinsic acitivity is unitless.  ED50 values are commonly encountered in scientific notation, e.g. 1.5x10-3.  Currently, this applet only accepts numbers in decimal format, e.g. 0.0015.

Drug (Color) Efficacy ED50
one (blue)
two (red)
three (green)
calculation may be slow

Problem information - see also the dose-response applet

The data for three agonists and partial agonists are shown in the table below.  Use this data to answer the following questions.

Drug Efficacy ED50
A 1.0 0.005
B 0.5 0.005
C 1.0 0.00005

Problems

The treatment in the two questions below is identical to the first two questions of the dose-response applet.  Differences that are unclear in a dose-response plot are often clearer in a log(dose)-response plot.

  1. Using the applet, generate a dose-response plot for all three drugs.  Between drug A and B, which is the better agonist?  Explain your answer.

  2. Between drug A and C, which is the better agonist?  Why?