Two antihypertensives are compared in dose-response studies. Drug X lowers blood pressure maximally by 30 mmHg with an EC50 of 0.1 mg/kg. Drug Y lowers blood pressure maximally by 30 mmHg with an EC50 of 5 mg/kg. Which statement is correct?
- A Drug X is more potent than drug Y, and both have equal efficacy ✓
- B Drug Y is more potent than drug X
- C Drug X is more efficacious than drug Y
- D Drug Y has a steeper dose-response curve than drug X
Correct answer: A. Drug X is more potent than drug Y, and both have equal efficacy
Explanation
Potency is reflected by position along the dose axis: the lower EC50 of drug X means less drug is needed for the same effect, so X is more potent. Efficacy is the maximal effect, identical here at 30 mmHg. Clinically, a more potent drug is not necessarily better; efficacy, safety and cost usually matter more. The distinction between potency (EC50) and efficacy (Emax) is repeatedly examined and frequently confused by examinees.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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