DRUG RECEPTOR INTERACTIONS

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DRUG RECEPTOR INTERACTIONS

• Roselyn Aperocho-Naranjo
• Pharmacy Instructor
• University of Southern Philippines Foundation
• www.roselynnaranjo.vze.com

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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

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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

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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.

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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.

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Definition of Terms

• Antagonist molecules that acts against and
  blocks
• drug action

Receptor
receiver
action
Agonist
Antagonist
against
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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

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Types of Antagonism

• Partial Antagonism
• Antagonist has high affinity but low intrinsic
  activity
• Non-equilibrium Antagonism
• Antagonist forms irreversible receptor binding
• Noncompetitive Antagonism
• Agonist and antagonist bind to different
  receptors and have opposite pharmacologic actions

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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.

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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

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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.

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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.

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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.

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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.

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GOOD LUCKand Prepare ½ crosswise.