Welcome to pharmacology by Lecturio.
Today's topic is pharmacodynamics.
We are going to evaluate and see how drugs move through
the body in pharmacodynamics.
Let's go over a couple of definitions.
Excretion is the physical removal of drug from the body.
So for example, we're excreting drug into the urine, or into
the bile, or exhaling inhalational drugs.
Elimination is a biochemical process without actual removal.
So, eliminating a drug means that the drug may
still be in the body, but you've rendered it somehow
different through a biochemical process.
A receptor is a specific protein on or in the cell that binds
to the drug to effect the change.
And effectors are molecules that effect a change as a result
of the receptor and drug binding together.
So, a receptor binds to the drug, and effector molecule
goes and does the job of the drug.
Affinity refers to the strength of the bond between a drug
And selectivity refers to the proportion of or a preference
of a receptor has for a particular drug.
It's usually compared to another similar kind of receptor,
for example, we may have selectivity for the alpha 1 receptor
versus the alpha 2 receptor,
and the selectivity ratio may be 1000:1.
Specificity refers to the amount of preference
a receptor has for a particular drug.
So, it's usually thought of as a comparator to another drug.
So for example, one drug might be more specific
to a receptor than a second drug.
Agonism refers to the ability to activate the mechanisms to
cause an effect.
And antagonism is the ability to inhibit the mechanism
to cause a biologic effect.
Efficacy refers to the maximum effect of a drug
at its highest tolerated dose.
Well, potency is a measurement of the amount of drug
needed to cause an effect.
So, a drug may have a high efficacy but a low potency.