EC50 represents the concentration of a drug that produces what percent of the maximal effect?

EC50 represents the concentration of a drug that produces what percent of the maximal effect?

• A. 100% of the maximal effect
• B. 25% of the maximal effect
• C. 50% of the maximal effect
• D. 0% of the maximal effect

Answer: (C)

EC50 is the concentration of a drug that yields half of its maximal response. On a typical dose–response curve, the point where the response is exactly half of the maximum (Emax) is the EC50, so the percent of the maximal effect at that concentration is 50%. This also ties to potency: a drug with a lower EC50 reaches 50% of its maximal effect at a lower concentration. In contrast, 0% is no effect, and 100% is full maximal effect, which occur at baseline and at high concentrations, respectively. If you think in terms of the math, at EC50 the response equals Emax/2.

EC50 is the concentration of a drug that yields half of its maximal response. On a typical dose–response curve, the point where the response is exactly half of the maximum (Emax) is the EC50, so the percent of the maximal effect at that concentration is 50%. This also ties to potency: a drug with a lower EC50 reaches 50% of its maximal effect at a lower concentration. In contrast, 0% is no effect, and 100% is full maximal effect, which occur at baseline and at high concentrations, respectively. If you think in terms of the math, at EC50 the response equals Emax/2.