DRUG RECEPTOR
INTERACTIONS
Roselyn Aperocho-Naranjo
Pharmacy Instructor
University of Southern Philippines Foundation
www.roselynnaranjo.vze.com
Definition of Terms

Receptors – are chemicals which binds to the drug to
exert a pharmacologic effect.
Formula:
D + R = D-R ------ Drug Response
Note: Binding of a drug to the receptor is usually reversible
A Receptor is analogous to
a switch in that it has two
configurations: “ON” and “OFF”
Definition of Terms

Receptor
Four Primary Receptor Families
1. Cell-membrane embedded proteins
2. Ligand-gated Ion Channel
3. G –protein coupled Receptor Systems
4. Transcription Factors
Definition of Terms

Agonist – are molecules that activates receptors.
- a drug that has both affinity and high
intrinsic activity.
Many drugs produce their effects
by acting as an agonist.
For example:
DOBUTAMINE - it mimics the action of
norephenephrine at the receptors on the
heart. Thereby causing the heart to contract
and increase the heart beat.
Definition of Terms

Affinity – allows the agonist to bind to receptors.

Intrinsic Activity – allows the bound agonist to
activate or turn on its receptor
function.
Definition of Terms

Antagonist – molecules that acts against and blocks
drug action
Types of Antagonism

Chemical Antagonism


Interaction of drug (agonist) with another chemical
(antagonist) outside of receptor to form an inactive
complex.
Competitive Antagonism



Drug (agonist) is displaced from drug-receptor binding by
another chemical (antagonist).
It is reversible and depends on actual drug and antagonist
concentration in the biophase.
Law of mass action
Types of Antagonism

Partial Antagonism


Non-equilibrium Antagonism


Antagonist has high affinity but low intrinsic activity
Antagonist forms irreversible receptor binding
Noncompetitive Antagonism

Agonist and antagonist bind to different receptors
and have opposite pharmacologic actions
Types of Pharmacologic Action of the
Drugs

Structural Non-specific Drugs
- drugs which do not depend its pharmacologic
action to the chemical structure of the drug.
- only its structure affects its physicochemical
property.
- slight modification of its structure does not produce
a change in its pharmacologic action.
Types of Pharmacologic Action of the
Drugs

Structural Specific Drugs
- drugs in which the pharmacologic action directly
depend on its chemical structure
- it attaches itself to a receptor in the biophase
Three Prerequisites of the binding of
drug to the receptor
1. chemical reactivity
2. presence of functional group
3. electronic distribution
4. mirror-like image of the receptor
Drug-Receptor Theories

Hypothesis of Clark
“ The Pharmacologic effect of the drug depends on the
percentage of the receptors occupied”
If receptors are occupied, maximum effect is obtained.
Chemical binding follow the Law of Mass Action.
Drug-Receptor Theories

Hypothesis of Ariens and Stephenson
“ Effectiveness of a drug lasts as long as the
receptor is occupied. Many substance possess
different effect , some have high affinity for the
receptor, some have low affinity and some are not
effective, and those ineffective substances block or
inhibit the receptor.”
It is also called Occupation Theory.
Drug-Receptor Theories

Hypothesis of Paton
“ Effectiveness of a drug does not depend on
the actual occupation of the receptor but by
obtaining proper stimulus”
This is also known as the Rate Theory.
Drug-Receptor Theories

Lock and Key Hypothesis
“ The drug molecule must fit into the receptor
like a key fits into the lock”
Known as the Intrinsic Activity.
GOOD LUCK
and
Prepare ½ crosswise….