Learning objective
Distinguish potency, efficacy and antagonist curve changes using the axes and the measured endpoint.
Read the axes before naming a curve
A graded dose-response curve plots response magnitude against dose or concentration in a defined system. Potency concerns the dose or concentration needed for a specified effect; a leftward position can indicate greater potency for the same endpoint. Efficacy concerns the maximal response attainable in that system. A higher plateau means greater maximal response, not necessarily greater potency. A steep region means a small dose change can produce a relatively large response change.
Full, partial and neutral antagonist
A full agonist reaches the system’s reference maximum. A partial agonist reaches a lower maximum in that same comparison even as its concentration increases. A neutral antagonist blocks agonist action without producing its own agonist response. A partial agonist is defined by lower efficacy, not necessarily lower potency. The book’s page 53 uses “less potent” loosely; its Chapter 3 curves and the supplementary Assay Guidance Manual support keeping these terms separate.
Competitive and insurmountable patterns
In a simple equilibrium model, a reversible competitive antagonist shifts an agonist curve rightward; more agonist is needed but the same maximum can be reached. An insurmountable blockade can lower the attainable maximum. The book illustrates a noncompetitive/irreversible pattern, but “noncompetitive” and “irreversible” describe different properties. Real curve interpretation also depends on assay conditions and receptor reserve. These idealized patterns are reasoning aids rather than dosing rules.
| Curve | Concentration for half of its own maximum | Maximum response |
|---|---|---|
| A | 2 model units | 100 response units |
| B | 8 model units | 100 response units |
| C | 1 model unit | 40 response units |
Check your understanding
Supplemental knowledge check
Original PolyDiscipline practice based on the explanation and cited sources. Unscored; answers are temporary to this page visit and do not award mastery or XP.
Supplemental knowledge check
Original PolyDiscipline practice based on the explanation and cited sources. Unscored; answers are temporary to this page visit and do not award mastery or XP.
Explain it without notes
How could a partial agonist reduce the effect of a full agonist?
Compare your explanation 1
If it competes for the same receptors, it can replace some full-agonist occupancy with lower-efficacy activation. The result depends on the mixture and system.
Distinguish competitive from reversible.
Compare your explanation 2
Competitive describes competition at a binding site; reversible describes whether binding can dissociate. They answer different mechanistic questions.
Revisit the connected course lessons and visuals
Julien’s Primer of Drug Action, supplied consolidated PDF pages 37, 38, 39 (Chapter 3). Locators refer to PDF captures, not printed pages. Original paraphrase and practice; source conformance reviewed, not independently clinically certified. Professor or supplementary clarifications are identified in the lesson and source list.