Elementary tools of Pharmacodynamics


Receptors: protein molecules including enzymes, transporters and ion channels where a ligand (specific endogenous neurotransmitter/hormone or an external pharmacological agent (drug)) binds to, resulting in a cellular response.

  • Unique Exception: Orphan Receptors are receptors for which the ligand remains unknown.
  • Reminder: Ligand is an ion or molecule that forms a complex with a biomolecule to serve a specific biological purpose

DRUG: A chemical agent that selectively interacts with specific target molecules (i.e. receptors) to alter their specific physiological functions.

  • Agonist: drug that activates receptors to result in either stimulation or inhibition of the function of various types of cells and organs.
  • Antagonist: drug that prevents receptor activation by agonists.

Drug-Receptor Binding: drugs bind to their respective receptor in a variety of ways depending on their characteristics.

  • Ionic interaction: cation & anion
  • Hydrogen bonding
  • Lipophilic interaction
  • Covalent bond: irreversible

FACTORS GOVERNING DRUG ACTION: All drugs are chemicals but not all chemicals are drugs.   For a drug to produce a physiologic effect it must first bind to a receptor.  Two factors, related to the chemical nature of a drug, determine the interaction of drugs with receptors and hence the effect a drug will have on physiologic processes.

  • Affinity is a measure of the tightness with which a drug binds to the receptor.
  • Intrinsic activity is a measure of the ability of a drug that is bound to the receptor to generate an activating stimulus and produce a change in cellular activity.
  • Both agonists and antagonists can bind to a receptor. However, only agonist molecules can activate the receptor.

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Angelina Matthew,

Managing Editor,

Pharmaceutical Analytical Chemistry

Email id: pharmachem@scholarlypub.com