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DRUG ANTAGONISM

DRUG ANTAGONISM. DR. SHABANA ALI. DRUG ANTAGONISM. One drug or inhibits action of another drug Types of Antagonism Physical antagonism Chemical antagonism Physiological/functional antagonism Pharmacological antagonism. A) Physical Antagonism.

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DRUG ANTAGONISM

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  1. DRUG ANTAGONISM DR. SHABANA ALI

  2. DRUG ANTAGONISM One drug or inhibits action of anotherdrug Types of Antagonism • Physical antagonism • Chemical antagonism • Physiological/functional antagonism • Pharmacological antagonism

  3. A) Physical Antagonism • Based on physical property of drugs, e.g. charcoal (adsorb alkaloid) in alkaloidal poisoning B) Chemical Antagonism • Chemical reaction between two drugs • e.g., NaHCO3 HCl

  4. C) Physiological/Functional Antagonism Opposite effects of two drugs on same function • Two drugs act on two diff. types of receptors & antagonize action of each other, e.g. histamine & adrenaline (adrenaline for treatment of anaphylactic shock); Ad & insulin on blood sugar level

  5. D) Pharmacological Antagonism • Opposite effect of two drugs binding to same receptors • Receptor antagonism is specific,e.g. atropine  spam of intestine by acetylcholine not by Hist.or 5-HT Types Competitive Non-competitive Equilibrium Non-equilibrium (Reversible) (Irreversible)

  6. i) Competitive Antagonism (equilibrium or reversible) Competition between agonist & antagonist for specific site or receptor • Action of agonist is blocked if conc. of antagonist is  • Antagonism can be overcome (surmount) by  conc. of agonist Cont.

  7. Agonist can produce max.response in higher conc. • Competitive antagonist shifts log Dose-response curve of agonist to right • EC50 of agonist  in presence of antagonist, e.g., Ach & atropine; Ad & Prop.; Morphine & naloxone

  8. COMPETITIVE ANTAGONISM

  9. II) Non-Equilibrium(irreversible) Antagonist • Antagonist binds to receptor with covalent bond • Irreversible blocking • Antagonist shifts DRC to right+  max. response, e.g. adrenaline & phenoxybenzamine

  10. iii) Non-competitive (non-surmountable Antagonist • Antagonist binds to another site of receptor • DRC is flattened + max. response is  • e.g., verapamil (noradrenaline)

  11. Non-competitive Antagonist

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