Drug
antagonism
Definition(Drug
antagonism):The effect of one drug can be
reduced or abolished by the presence of another drug.This called drug
antagonism.
Types:Drug
antagonism is of 3 types:
a)
Chemical antagonism.
b)
Physiological
antagonism.
c)
Pharmacological
antagonism.
[A]Chemical
antagonism:When a drug antagonizes the effect
of another drug by simple chemical reaction,it is called chemical
antagonism.Here recptors are not involved.
·
Antacid+Gastric
acid→Neutralization of gastric acid→↓Mucosal irritation→↓pain.
[B]Physiological
antagonism:When a drug antagonizes the effect
of another drug by acting or two
different types of receptors of the same physiological system,it is
called physiological antagonism.e.g
|
Drug
|
Bronchus
|
Blood vessels
|
Heart
|
Eye
|
|
1.Ach(cholenergic re)
|
Bronchoconstriction
|
Vasodilatation
|
↓HR&↓FOC
|
Myosis
|
|
2.Histamine
|
Bronchoconstriction
|
Vasodilatation
|
↑HR&↑FOC
|
|
[C]Pharmacological
antagonism: When a drug antagonizes the effect
of another drug by acting the same receptor,it is called pharmacological
antagonism.It is two types:
(a)Competitive/Surmountable
antagonism:
1)
Both the agonist &
antagonist compete for the same receptor & able to displace each other from
the recptor site.
2)
It is revrsible.
3)
It is dose
dependent/conc of drug dependent.
**Example:Ach&Atropine,Histamine&Antihistamine.
**Clinical
significance:
1)
For specific antidote
purpose in case of acute poisoning.e.g Atropine in OPC poisoning.
2)
For Rx of disease.e.g
antacid in peptic ulcer.
3)
To correct the adverse
effect of drug.e.g Histamine+Antihistamine.
(b)Non-competitive:Non-copetitve
antagonism is irreversible.It is not surmountable.
**Cause:
·
Antagonist-re
complex→Covalent bond(Strong bond)→No of re decreased→Less drug action.
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