Question

Plasma protein bound drugs are:

• A. Pharmacodynamically active
• B. Pharmacokinetically inert
• C. Pharmacokinetically and Pharmacodynamically inert
• D. Pharmacodynamically inert

Hint:

Only the free drug fraction is pharmacodynamically active. Plasma protein binding extends drug half-life but delays immediate pharmacological effects.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Plasma protein binding separates a drug dose into a free fraction and a bound fraction. Pharmacodynamics is about receptor action, and pharmacokinetics is about how the drug moves through the body, and the bound fraction behaves differently under each.

Step 2: Key Fact:
The receptor site cannot be reached by a drug still attached to a large plasma protein, so the bound fraction produces no pharmacological effect, making it pharmacodynamically inert. It still matters pharmacokinetically, since it acts as a reservoir that slowly releases free drug and extends the drug's presence in the body.

Step 3: Detailed Explanation:
Calling the bound drug pharmacodynamically active is wrong because binding blocks receptor access.
Calling it pharmacokinetically inert is wrong because binding changes distribution and slows elimination.
Calling it inert on both counts is wrong for the same pharmacokinetic reason.
Only the option that keeps pharmacokinetic activity while removing pharmacodynamic activity fits how protein binding actually works.

Step 4: Final Answer:
Plasma protein bound drugs are pharmacodynamically inert.