Drug X produces half of its own maximal effect at a dose of 1 mg. Drug Y needs 100 mg to produce half of its own maximal effect, yet the highest response attainable with Y far exceeds that of X. Compared with drug Y, drug X has:

• A Greater potency and lesser efficacy ✓
• B Greater potency and greater efficacy
• C Lesser potency and greater efficacy
• D Lesser potency and equal efficacy

Explanation

Potency is reflected by the position of the dose-response curve on the dose axis: X acts at 1 mg against 100 mg for Y, so X is far more potent. Efficacy is reflected by the ceiling of the curve: Y reaches a higher maximal effect, so Y is more efficacious. Exams repeatedly test that a potent drug need not be the clinically superior one, because efficacy limits achievable benefit.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.