In comparing multiple dose-response curves, which curve corresponds to the most potent drug?

In comparing multiple dose-response curves, which curve corresponds to the most potent drug?

• A. The curve with the highest Emax
• B. The curve with the steepest slope
• C. The curve with the largest dose required for maximal effect
• D. The curve with the lowest EC50 (leftmost)

Answer: (D)

Potency is about how much drug is needed to produce a given effect—the smaller the dose, the more potent the drug. In dose–response curves, the EC50 value (the dose producing 50% of the maximal effect) captures potency: the curve that reaches 50% effect at the lowest dose is the most potent, i.e., the leftmost curve. The curve with the highest maximal effect (Emax) speaks to efficacy, not potency. A drug can have a very high Emax but require a larger dose to start producing effects, so it isn’t necessarily the most potent. The steepest slope reflects how rapidly response increases with dose (sensitivity), not the dose needed for a given effect. The curve requiring the largest dose to achieve maximal effect indicates lower potency. Therefore, the curve with the lowest EC50, the leftmost curve, is the most potent.

Potency is about how much drug is needed to produce a given effect—the smaller the dose, the more potent the drug. In dose–response curves, the EC50 value (the dose producing 50% of the maximal effect) captures potency: the curve that reaches 50% effect at the lowest dose is the most potent, i.e., the leftmost curve.

The curve with the highest maximal effect (Emax) speaks to efficacy, not potency. A drug can have a very high Emax but require a larger dose to start producing effects, so it isn’t necessarily the most potent. The steepest slope reflects how rapidly response increases with dose (sensitivity), not the dose needed for a given effect. The curve requiring the largest dose to achieve maximal effect indicates lower potency. Therefore, the curve with the lowest EC50, the leftmost curve, is the most potent.