1. DRUG ANTAGONISM
DR. SHABANA ALI

2. DRUG ANTAGONISM One drug or inhibits action of another drug
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., NaHCO 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