Drug-receptor theories - ANTAGONIST

Drug-receptor interactions- Antagonists

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  • Created by: Sophie
  • Created on: 13-01-13 17:16
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  • Drug-receptor theories - ANTAGONIST
    • Clinical Uses
      • Drug
        • Proprolol
          • B-antagonist
            • antihypertensive
        • Metaprolol
          • B-antagonist
            • antihypertensive
        • Prazosin
          • a-antagonist
            • antihypertensive
        • Atropine
          • muscarinic antagonist
            • Parkinson's Disease
    • Drug Antagonism
      • Chemical antagonishm
        • Uncommon
        • 2 substances combine in solution; as a result, the effect of active drug is lost
        • eg. Dimercaprol binds to heavy metal to reduce toxicity
        • eg. Ca/Mg binds to tetracycline antibiotics in gut
      • Pharmacokinetic Antagonism
        • One drug lowers the concentration of another; antagonish lowers concentration of active drug
          • Reduced Absorption
          • Increased metabolism
          • Increased excretion
      • Receptor Antagonism
        • Antagonist binds to receptor but theres not biological response
        • Effect of antagonist is blocked
        • Agonist and antagonist can bind to same site
        • Some receptors are multi-protein complex
        • Agonist or antagonist may bind to diff. proteins or diff. sites on the same protein
        • 3 types of receptor antagonism
          • Non-competitive
            • Antagonist blocks events initiated by agonist
            • Antagonist does not bind to same site as agonist
          • Irreversible/ Non-equilibrium
            • Drug binds to receptor active site but does not dissociate because:
              • Covalent Reaction
              • Very very slow dissociation
            • Active site is occupied by antagonist so agonist cannot bind
              • Addition of agonist does not change the no. of receptors occupied by antagonist
          • Competitive
            • Most common
            • Agonist and antagonist compete for same receptor site
            • Reversible binding so dynamic competition
            • Drug receptor theory
              • 2 equations:
                • D + R <=> DR
                  • A + R <=> AR
                    • -X response
                      • Both agonsit (D) and antagonist (A) are present and competing for same binding site on receptor (R)
                  • -> response
                    • Both agonsit (D) and antagonist (A) are present and competing for same binding site on receptor (R)
                    • -X response

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