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Chapter 2 : Pharmacodynamics

Topics covered in this snack-sized chapter:

Pharmacodynamics arrow_upward

  • Pharmacodynamics means the action of a drug on the body, including receptor interactions, dose-response phenomena, and mechanisms of therapeutic and toxic action.
  • Principles of Drug Actions:
    • Drugs do not introduce any new functions in body system; they only produce alteration of present activity of body functions.
  • Actions are classified as follows:
    • Stimulation
    • Depression
    • Irritation
    • Replacement
    • Cytotoxic Action
  • Mechanism of Drug Action:
    • Drugs produce their effects by acting on discrete target biomolecule known as proteins.
    • Targeted functional proteins are of 4 types:


    Enzyme inhibition is a common mode of drug action.

    Ion Channels

    Drugs can affect ion channels either through specific receptors or by binding to the channel directly.


    Drugs produce their action by directly interacting with the solute carrier class of transporter proteins to inhibit the ongoing physiological transport of the metabolite/ion.


    Majority of drugs produce action by interaction with specific macromolecules known as receptors.

  • The following terms are used in     describing drug-receptor interaction:
    • Agonist: An agent which activates a receptor to produce an effect.
    • Inverse agonist: An inverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist.
    • Antagonist: An agent which prevents the action of an agonist on a receptor or the subsequent response, but does not have any effect of its own.
    • Partial agonist: An agent which activates a receptor to produce sub maximal effect but antagonizes the action of a full agonist.
    • Ligand: Any molecule which attaches selectively to particular receptors or site.

    Diagramatic Depiction of Mechanism of Drug Action

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