Action Effect Sequence

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Chapter: Essential pharmacology : Pharmacodynamics Mechanism Of Drug Action; Receptor Pharmacology

‘Drug action’ and ‘drug effect’ are often loosely used interchangeably, but are not synonymous.


ACTION EFFECT SEQUENCE

 

‘Drug action’ and ‘drug effect’ are often loosely used interchangeably, but are not synonymous.

 

Drug Action

It is the initial combination of the drug with its receptor resulting in a conformational change in the latter (in case of agonists), or prevention of conformational change through exclusion of the agonist (in case of antagonists).

 

Drug Effect

It is the ultimate change in biological function brought about as a consequence of drug action, through a series of intermediate steps (transducer).

 

Receptors subserve two essential functions, viz, recognition of the specific ligand molecule and transduction of the signal into a response. Accordingly, the receptor molecule has a ligand binding domain (spatially and energetically suitable for binding the specific ligand) and an effector domain (Fig. 4.4) which undergoes a functional conformational change. These domains have now actually been identified in some receptors. The perturbation in the receptor molecule is variously translated into the response. The sequential relationship between drug action, transducer and drug effect can be seen in fig 4.6.

 


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