Drug
receptor: Drug receptors are the macromolecular protein
in nature situated in the cell surface pr inside the cell which has
chemorecognition properties for specific drug with which reversibly or
irreversibly binds.
Efficacy:The
effect produced by drug is called efficacy.
·
Amiloride cause
5%
excertion→Low efficacy.
·
Thiazide cause
10%
excertion→Moderate efficacy.
·
Frusemide cause
25%
excertion→High efficacy.
Potency: Any
response or effect of a drug by a fixed dose is called potency.It is expressed
in w/w.Potency is influenced by-
·
Absorption.
·
Distribution.
·
Biotransformation.
·
Excertion of drug
Difference
between potency & efficacy:
|
Potency
|
Efficacy
|
|
1.Potency does not help to choose among drug.
|
1.Efficacy help to choose among drugs.
|
|
2.Potency determine the administered dose of the
choosen drug.
|
2.Efficacy determine clinical effectiveness of a
drug.
|
|
3.Potency≡Affinity
|
3.Efficacy≡Intrinsic activity
|
|
4.Potency is affected by affinity of receptors for
binding the drug and also by efficiency of drug receptor interactions.
|
4.Efficacy may be affected by the characteristics of
a particular drug receptors interaction.
|
|
5.Clinical significance:important in durgs of low
theraputic index.
|
5.Important in clinical effectiveness of a drug
|
Agonist
drug:
·
Affinity to
receptor:+++
·
Efficacy:+++
·
Definition:A drug that binds with receptor and activite
them to produce a pharmacological response is called agonist.
·
Example: Pilocarpine(Muscarinic
agonist),Sulbutamol(β-adrenoceptor agonist)
Antagonist
drug:
·
Affinity to
receptor:+++
·
Antagonist has no
efficacy.
·
Definition:Drugs that bind with receptor (as agonist)but
no activating effect are termed pure antagonist.
·
Example:Propanolol(β-adrenoceptors
antagonist),Atropine(Muscarinic antagonist),
Naloxane(Morphine antagonist).
Difference between Agonist & Antagonist:
|
Receptor
|
Agonist
|
Antagonist
|
|
[A]Cholinoceptors
|
|
|
|
Muscarinic
|
Ach/Muscarine
|
Atropine
|
|
M1
|
Muscurine
|
Piperazine
|
|
M2
|
Bethanechol
|
|
|
Nicotinic
|
Ach/Nicotine
|
Hexamethonium(for ganglia)
|
|
N1
|
Di-methylphenyl piperazine
|
Hexamethonium
|
|
N2
|
Phenytrimethyl ammonium
|
D-tubocurarine
|
|
[B]Adrenoceptors
|
|
|
|
α adrenoceptors
|
NA
|
Phenoxybenzamine
|
|
α 1
|
Phenylephrine
|
Prazosine
|
|
α 2
|
Clonidine
|
Yohibine
|
|
Βadrenoceptors
|
Adrenaline/Isoprenaline
|
Propranolol
|
|
β 1
|
Dobutamin
|
Metoprolol
|
|
β 2
|
Sulbutamol/Terbutaline
|
Butoxamine
|
|
[C]Histaminergic receptor
|
|
|
|
H1
|
Histamin
|
Chlorpheniramine
|
|
H2
|
Histamin
|
Cimetidine/Ranitidine
|
|
[D]Serotonergic recptors
|
|
|
|
5-HT1
|
5-HT
|
Methysegride
|
|
5-HT2
|
5-HT
|
Spiroperidol
|
Partial
agonist:
·
Affinity to
receptor:+++
·
Efficacy less
than true agonist.
·
Definition:Drugs that bind with receptor and capable of
low degree of activating of receptors.
·
Example:Clonidine,Nalorphin,Pindolol,Acebutol.
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