The dose-response curve typically plots which relationship?

• A. % maximal response versus drug concentration or log drug concentration.
• B. Drug bound versus log concentration of agonist.
• C. Time to reach maximum effect.
• D. Efficacy versus receptor number.

Answer: (A)

Dose-response relationships show how the magnitude of a drug’s effect changes as you increase the dose. The typical plot displays the percent of the maximal response achieved (often normalized to 0–100%) on the y-axis, while the drug concentration (or its logarithm) is on the x-axis. This normalization lets you compare across different drugs and experiments and lets you extract key parameters like Emax (the maximum effect) and EC50 (the concentration that produces 50% of the maximum effect).

The reason this is plotted against concentration (or log concentration) is that the response scales with how many receptor units are engaged by the drug, and the relationship often follows a sigmoidal shape described by the Hill equation, reflecting cooperative binding or other mechanisms amplifying the response at intermediate concentrations.

Why the other ideas don’t fit: a binding curve showing drug bound versus log concentration measures receptor occupancy, not functional effect. Time to reach maximum effect is a kinetic consideration, not the dose-response relationship itself. Efficacy versus receptor number shifts topics to receptor theory and occupancy, not the direct dose-to-response relationship.