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Drug shape

• The shape of the drug is an important factor in defining the nature of the drug-receptor interaction.  The three-dimensional shape of the drug is thought to interact with a complementary structural binding region of the receptor, typically a protein.  The specific nature of the interaction defines whether the drug acts as an agonist promoting a change in cellular function or as an antagonist which blocks the receptor usually resulting in no direct biological effect.

  • For example, let's consider acetylcholine or a synthetic analogue bethanechol (Urecholine). 

    • Interaction of these molecules with receptor (nicotinic or muscarinic cholinergic receptor) causes a physiological response, for example, a decrease in heartbreak for instance. 

    • By contrast, a muscarinic antagonist such as atropine may bind even more tightly than acetylcholine to muscarinic receptor but causes no direct effect. 

      • However, following administration of antagonist a biological response may be observed as a result of receptor blockade.  

    • A clinical example would be bradycardia following acute myocardial infarction. 

      • Bradycardia in this context might be due to excessive parasympathetic (cholinergic) tone and might cause unacceptably low cardiac output or predispose to more serious arrhythmias. 

        • Administration of atropine, by blocking the muscarinic receptor blunts the action of acetylcholine and accordingly may reverse bradycardia.

• Now let's consider the specific example, acetylcholine, as the 2D planar structure:

  • Acetylcholine