Which statement about dose–response curves is true?

Which statement about dose–response curves is true?

• A. A graded dose–response is continuous; a quantal dose–response relates dose to frequency.
• B. A graded dose–response is all-or-none; a quantal dose–response is continuous.
• C. Both graded and quantal dose–response relationships are always identical in interpretation.
• D. Potency can be inferred only from the area under the curve for graded responses.

Answer: (D)

Graded versus quantal dose–response relationships describe two different ways we think about drug effects. A graded curve shows how the magnitude of a response in a single individual changes smoothly as the dose increases; it’s continuous and lets you see exactly how much effect you get at each dose. A quantal curve, on the other hand, looks at a population: at each dose, you ask what fraction of individuals show a defined effect. That relation is dose versus frequency (proportion). Potency is about how much drug you need to produce a given effect. For graded responses, we typically use the EC50—the dose that produces 50% of the maximal effect. For quantal responses, we use the ED50—the dose at which 50% of individuals show the effect. The area under the curve is not the measure of potency; it reflects overall exposure or total response across doses, not the specific dose needed for a defined effect. So the key idea is that graded curves are continuous within an individual, quantal curves relate dose to the frequency of response across a population, and potency is inferred from the dose producing a given level of effect (not from the area under the curve).

Graded versus quantal dose–response relationships describe two different ways we think about drug effects. A graded curve shows how the magnitude of a response in a single individual changes smoothly as the dose increases; it’s continuous and lets you see exactly how much effect you get at each dose. A quantal curve, on the other hand, looks at a population: at each dose, you ask what fraction of individuals show a defined effect. That relation is dose versus frequency (proportion).

Potency is about how much drug you need to produce a given effect. For graded responses, we typically use the EC50—the dose that produces 50% of the maximal effect. For quantal responses, we use the ED50—the dose at which 50% of individuals show the effect. The area under the curve is not the measure of potency; it reflects overall exposure or total response across doses, not the specific dose needed for a defined effect.

So the key idea is that graded curves are continuous within an individual, quantal curves relate dose to the frequency of response across a population, and potency is inferred from the dose producing a given level of effect (not from the area under the curve).