bind to receptors and produce a response- effects of various types 2. Antagonists bind to receptors without producing a response and by occupying the receptors they prevent action of agonists.

1. Principles of
pharmacodynamics
Adnan mansour jasim
alqasim green university

2. Receptors

3. Regulatoryproteins–receptors
drugsactonreceptorsasagonistsorantagonists
1. Agonists
bind to receptors and produce a response-
effects of various types
2. Antagonists
bind to receptors without producing a response and by
occupying the receptors they prevent action of agonists.

5. 1. Agonists (cont.)
• Affinity - tendency to bind to the receptors (attraction
between receptor and drug)
• Efficacy - ability once bound, to initiate changes,
which lead to effect (is the capacity of drug to activate
a receptor)
Full agonists - can produce maximal effect when all
receptors are occupied (high efficacy)
 Partial agonists - can produce only submaximal
effects even when all receptors are occupied

7. 2. Antagonists
• competitive antagonism
 antagonists are able to displace the agonists from the
receptors (one drug can be displaced by another drug),
 may be abolished by adding an excess of agonist.
a. reversible
b. ireversible
antagonist dissociates very slowly or not

8. 2. Antagonists (cont.)
non-competitive antagonism
a. form bonds with the receptors usually at sites other
than the endogenous agent.
b. in some cases binding may be covalent and ireversible
c. cannot be overcom by higher concentration of agonist

10. Log-concentration-effect curve
c
10-8
10-7 10-6 10-5 10-4
potency (affinity)
50%
EC50
efficacy
slope of the curve

11. Typical dose-response
curve for drug showing
differences in potency
and efficacy.
(EC50 = drug dose that
shows fifty percent of
maximal response.)
Drug A is more potent
than Drug B, but both
show the same efficacy.
Drug C shows lower
potency and lower
efficacy than Drugs A
and B.
Drug A Drug B
Drug C
Log drug concentration
EC50
for
Drug A
EC50
for
Drug B
EC50
for
Drug C
0
50
100
Biologiceffect
(according to Lippincott´s
Pharmacology, 2006)

12. Therapeutic index
The ratio of the dose that produces toxicity to the dose that produces a
clinically desired or effective response in a population of individuals:
Therapeutic index = LD50/ED50
or TD50/ED50
TD50 = the dose that produces a toxic effect in half the population,
LD50 = the dose that produces a death in half the population
ED50 = the dose that produces a therapeutic or desired response in half the
population.
The therapeutic index = a measure of a drug's safety –
a large value = there is a wide margin between doses that are effective and
toxic.