Quantal dose-response curve plots what?

• A. The initial amount of drug in the body
• B. The rate of metabolism
• C. The time to response
• D. The fraction of the population that responds at each dose

Answer: (D)

Quantal dose-response curves show the fraction of a population that exhibits a predefined effect at each dose. This all-or-none response across individuals reflects variability in sensitivity among people. The y-axis represents the proportion of responders (from 0 to 1 or 0% to 100%), while the x-axis shows dose (often on a log scale). The curve is typically sigmoidal, and a key value is the dose that produces the effect in 50% of the population, known as the ED50. This framework lets you compare potency and safety by looking at how much drug is needed for a given percentage of people to respond.

The other ideas aren’t what this curve measures: it isn’t about the initial amount of drug in the body (that’s pharmacokinetics), the rate of metabolism, or the time to response (time-to-effect studies). The focus here is on the proportion of individuals who respond at each dose.