Competitive vs. noncompetitive antagonist
  • Competitive antagonist 
    • shifts agonist curve to the right
      • characteristics
        • resembles substrate [S]
        • blocks active site and can be overcome by ↑ [S]
        • ↓ potency, ↑ Km, and Vmax is unchanged
  • Noncompetitive antagonist  
    • shifts agonist curve downward
    • characteristics
      • does not resemble [S]
      • does not block active site, therefore no ↑ [S] can overcome effect
      • ↓ efficacy not potency, ↓ Vmax, and Km is unchanged
      • ↑ EC50 of agonist (half maximally effective concentration for producing a given effect)
Agonist vs. partial agonist
  • Agonist
    • acts on the receptor and triggers a full response (100% effect)
  • Partial agonist
    • acts on the same receptor as the full agonist
    • ↓ efficacy, independent of dose
    • may be more potent, less potent, or equally potent
      • potency is an independent factor
    • can compete with full agonist to inhibit some of the response of the full agonist
Synergism & Permissiveness
  • Synergism
    • the combined action of two drugs is greater than the activity of either alone (in total)
      • for example: monobactams and aminoglycosides
  • Permissiveness
    • drug A is required for the full effect of drug B to occur, it, "permits" drug B to work
      • cortisol/glucocorticoids and vasopressors

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