FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

Which type of antagonist does NOT affect the agonist's potency?

1. Competitive antagonist

2. Non-competitive antagonist

3. Inverse agonist

4. Partial agonist

The correct answer is: Non-competitive antagonist

A non-competitive antagonist works by binding to a different site on the receptor than the agonist. Its action doesn't interfere with the agonist's ability to bind to the receptor. Instead, it reduces the receptor's overall activity, regardless of how much agonist is present. This means that even if an agonist is at a high concentration, the effect will still be dampened because the receptor is unable to respond fully due to the presence of the non-competitive antagonist. As a result, the agonist's efficacy is reduced but not its potency, which is a measure of the concentration required to elicit a response. In contrast, a competitive antagonist directly competes with the agonist for the same binding site, which can affect the potency of the agonist by requiring a higher concentration to achieve the same effect. Inverse agonists and partial agonists also influence the agonist's potency differently, through mechanisms that involve either enhancing or modulating receptor activity in ways that change how effectively an agonist can exert its effects. Therefore, the non-competitive antagonist stands out as the choice that does not affect the agonist's potency because it alters the receptor's function rather than its ability to interact with the agonist.