Agonist and antagonist

Agonist and antagonist

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