In an efficacy versus concentration log chart, what does a higher plateau indicate?

In an efficacy versus concentration log chart, what does a higher plateau indicate?

• A. Greater efficacy
• B. Greater potency
• C. Faster onset of action
• D. Increased toxicity

Answer: (A)

The key idea is that the height of the plateau on an efficacy versus concentration curve represents the maximum effect the drug can produce (Emax). A higher plateau means the drug can achieve a greater maximal response, which is greater efficacy. Potency is about where the curve sits along the concentration axis (how much you need to reach a given effect), so it shifts the curve left or right but doesn’t change the plateau height. Onset of action and toxicity are not indicated by the plateau height on this plot—the plateau reflects efficacy, not how fast the effect starts or how toxic it might be.

The key idea is that the height of the plateau on an efficacy versus concentration curve represents the maximum effect the drug can produce (Emax). A higher plateau means the drug can achieve a greater maximal response, which is greater efficacy. Potency is about where the curve sits along the concentration axis (how much you need to reach a given effect), so it shifts the curve left or right but doesn’t change the plateau height. Onset of action and toxicity are not indicated by the plateau height on this plot—the plateau reflects efficacy, not how fast the effect starts or how toxic it might be.