Learning Objective
After this lesson, the learner will be able to distinguish between full and partial agonists and interpret their efficacy and potency using dose-response (D-R) curves.
Full Agonist
A drug that produces the maximal possible response when it binds to receptors. → Maximal efficacy
Partial Agonist
A drug that binds to the receptor but produces a submaximal response, even at high doses.
→ Lower efficacy than a full agonist
→ Can act as functional antagonists when competing with full agonists
Dose–Response (D-R) Curve Interpretation
Drug B → Full agonist
- Achieves the highest maximal effect
- Therefore has greater efficacy
Drugs A and C → Partial agonists
- Do not reach the same maximal effect as B
- Therefore, it has lower efficacy
Potency Relationships
- Drug A is more potent than Drug C
- Drug B is more potent than Drug C
- Drug A vs Drug B:
- Cannot directly compare potency because efficacy differs (partial vs full agonist)
- At low responses → A appears more potent
- At high responses → B is more potent
Potency is meaningful only when drugs have similar maximal effects (i.e., same efficacy category).