Pharmacology: Agonism and Antagonism

Agonism

• Definition: Occurs when a drug binds to a receptor and causes a biological response.
• Binding: Agonist drugs typically bind to the same place on the receptor as the endogenous substance (the natural activator).
• Types of Agonists:
  • Full Agonists: Generate a maximal response at a receptor.
  • Partial Agonists: Generate only a fraction of the possible response.
  • Inverse Agonists: Bind to a receptor and cause a decrease in signaling, producing effects opposite to those of an agonist.

Antagonism

• Definition: Occurs when a drug binds to a receptor but does not activate it, interfering with agonists' ability to activate the receptor.
• Types of Antagonism:
  • Reversible Competitive Antagonism:
    • A drug competes with an agonist for its binding site.
    • Limits the amount of agonist that can bind at the same time.
    • Antagonists unbind and rebind frequently, allowing effects to be overcome with more agonist.
  • Irreversible Competitive Antagonism (Noncompetitive Antagonists):
    • Bind to the agonist site but unbind very slowly, if at all.
    • Can reduce the maximal effect of an agonist, regardless of the amount present.

Allosteric Modulators

• Definition: Drugs that bind to a receptor at a different site from the agonist.
• Functions:
  • May increase or decrease the likelihood of an agonist binding.
  • Can enhance or reduce the effects of an agonist.
  • Might activate the receptor independently.