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1. Combined Effect of drug
When we use two drug in combination , then two
types of effects will be there -:
1. Synergism
2. Antagonism

2. Syn = Together
Ergon = Work
Synergism
When action of one drug is
increased by other drug
then this phenomenon is
known as synergism .
Additive
Supraadditive

3. 1.Additive effect -:
The effects of two drugs is in
same direction and simply adds up.
Effect of drugs BEffect of drug A +
Effect of drugs A+B
=
A
+
B
A

4. Example -:
1. Aspirin + Paracetamol
2. Nitrous Oxide + Halothane
# Side effects do not add up .

5. Effect of drugs BEffect of drug A +
Effect of drugs A+B
>
A
+
B
A
2. Supraadditive effect -:
The effect of combination is
greater than the individual effects of components.
Potentiation effect

6. Example
Drug pair Basis of Potentiation
1. Levodopa + Carbidopa Inhibition of peripheral metabolism
2. Adrenaline + Cocaine. Inhibition of Neuronal reuptake

7. When one drug decreases the
effect of another drug , this phenomenon known as
antagonism.
Effect of drugs BEffect of drug A +
Effect of drugs A+B
<
A
+
B
A
2. Antagonism -:

8. Antagonism
1. Physical Antagonism
2. Chemical Antagonism
3.Functional Antagonism
4. Receptor Antagonism

9. 1. Physical Antagonism -:
It is based on the physical
properties of drug. Example
Charcoal absorbs alkaloids - Used in alkaloidal poisoning.
2. Chemical Antagonism -:
Two drugs react
chemically and form an inactive product. Example
1. KMnO4 oxidizes alkaloids - used for gastric lavage in
poisoning.
2. Thiopental sodium + succinylcholine chloride

10. 3. Functional Antagonism -:
The two drugs act by different mechanism , but have opposite
effects on same physiological function.
Example
Glucagon & Insuline on blood sugar level.
4. Receptor Antagonism -:
Receptor -:
Receptor is macromolecule or binding site ,
present on the surface or inside the cell. Drug binds to
receptor and initiates response .

11. One Drug blocks the receptor
action of other drug .
Receptor Antagonism
Competitive Antagonism Noncompetitive Antagonism

12. Competitive Antagonism -:
The antagonist is chemically similar to agonist , competes
with it and binds to same site. Antagonist has no capacity
to produces response .
Example
Drug Competitive antagonist
Morphine Naloxone

13. Competitive Antagonism -:
Allosteric site Receptor
Agonist
Competitive antagonist

14. Competitive Antagonism -:
Allosteric site
Receptor
Agonist
Response

15. Competitive Antagonism -:
Allosteric site
Receptor
Competitive antagonist
No Response

16. Noncompetitive Antagonism -:
The antagonist is chemically unrelated to the agonist , binds
to allosteric site and alter the receptor in such a way that it is
unable to combine with the agonist or unable to produce
response.
NMDA Receptor Ketamine

17. Allosteric site Receptor
Agonist
Noncompetitive antagonist
Noncompetitive Antagonism -: