Two drugs act at the same receptor. Drug X has an EC50 of 0.1 mg/L with a maximal effect of 60 percent. Drug Y has an EC50 of 10 mg/L with a maximal effect of 95 percent. Which statement is correct?
- A Drug X is more efficacious than drug Y
- B Drug Y is more potent but less efficacious than drug X
- C Drug X is more potent, while drug Y is more efficacious ✓
- D Both drugs have equal potency and equal efficacy
Correct answer: C. Drug X is more potent, while drug Y is more efficacious
Explanation
Potency reflects the concentration needed to produce a given effect and is indicated by EC50, so drug X with the lower EC50 is more potent. Efficacy reflects the maximum attainable effect (Emax), which is higher for drug Y at 95 percent versus 60 percent. Students who equate potency with strength choose A or B, but potency says nothing about the ceiling of effect a drug can achieve.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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