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Dose-Response, Binding, Quantal, Toxicity & Potency Curves – Pharmacodynamics

by Pravin Shukle, MD
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    Let's go over response curves. This is going to be an important part of your exam. You need to be able to interpret these curves to give an answer. So let's take a look at a typical dose response curve. So on the vertical axis, you can see that this is the percent of maximum effect. And on the bottom, you have a log scale of the dose. So you can see here a competitive inhibitor. Your agonist is your drug alone, and you add the antagonist, and it causes an agonist plus competitive antagonist change or shift in the curve. So when we say that there's a shift in the dissociation or binding curve to the right, what we are really talking about here is that you've got some kind of competitive inhibitor. Compare this to a non-competitive inhibitor or an antagonist, so here you can see there's an agonist plus an irreversible antagonist. And what happens is your percent of activity is reduced by, in this case, 50 %, eventhough the dosages are starting out at the same point. So, notice the difference. The competitive inhibitor shifts the entire curve over to the right, the non-competitive inhibitor also called an allosteric inhibitor reduces the maximal impact of that particular drug, but starts at the same concentration. So, dose response curves can be logarithmic or non-logarithmic. Here is an example of the same drug portrayed in two different ways. The top is the absolute value, and the bottom scale here is the logarithmic value on the horizontal axis. The effective concentration that causes the maximal effect is called the Emax. So in both cases here, we have got the red line at 100 %. The effective concentration, or effective dose, that produces 50 % of the maximal effect is...

    About the Lecture

    The lecture Dose-Response, Binding, Quantal, Toxicity & Potency Curves – Pharmacodynamics by Pravin Shukle, MD is from the course Pharmacokinetics and Pharmacodynamics. It contains the following chapters:

    • Response Curves
    • Binding and Quantal Curve
    • Spare Receptors
    • Toxicity Curves
    • Potency Curves
    • Question to Potency Curves
    • Question: Pharmacologic Parameters

    Included Quiz Questions

    1. The binding affinity of the new drug is much higher than the binding affinity of the old drug.
    2. The strength of the new drug is greater than the strength of the old drug.
    3. The toxicity of the new drug is definitely greater than the toxicity of the old drug.
    4. More people in a population will respond to the new drug than the old drug.
    1. Make each tablet 325 mg, with the recommendation to take one to two tablets. Half of people will respond to 325 mg, and almost all people will respond to 650 mg.
    2. Make each tablet 325 mg, because most people will respond to 325 mg.
    3. Make each tablet 325 mg. The toxic dose is 650 mg. You should only take one pill per day.
    1. Jill has taken a medication to which she possesses spare receptors.
    2. Jill has taken a medication that is not effective.
    3. Jill has taken a medication that has a high binding affinity but a low effectiveness.

    Author of lecture Dose-Response, Binding, Quantal, Toxicity & Potency Curves – Pharmacodynamics

     Pravin Shukle, MD

    Pravin Shukle, MD


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