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Theories of drug receptor interaction

Receptor Theories

Discuss theories of drug receptor interaction
There are three major theories for drug-receptor interaction. They are as follows:
(i) Occupation theory
Occupation theory advocates that effect of a drug is directly proportional to the number of receptors which are occupied. Further, it is argued that a drug effect caeses as a drugreceptor
complex dissociates. The theory introduces towards: affinity and efficacy to indicate following meaning.
Affinity is the ability of a drug to combine with receptor to create a drug-receptor complex.
Efficacy is the ability of a drug-receptor complex to initiate a response.
(ii) Rate theory
In contrast to occupation theory, rate theory proposes that the activation of receptors is directly proportional to the number of encounters of a drug with its receptors per unit time. Pharmacological activity is directly proportional to the rates of dissociation and association and not on the number of receptors occupied. Thus, it is the rate at which drug-receptor complex is formed/dissociated which decides the quantum of response. In light of this theory; agonist, partial-agonist and antagonist can be identified as indicated below:
Agonist is a drug with fast association and fast dissociation. Partial agonist is a drug with an intermediate association and an intermediate dissociation. Antagonist is a drug with fast association and slow dissociation.
(iii) Induced-fit theory
According to induced-fit theory, as a drug approaches to a receptor, the receptor alters
the conformation of its binding site to produce drug-receptor complex.