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 plasma protein binding. Many drugs bind to plasma proteins, primarily albumin. Only the free (unbound) drug is available for pharmacological action. The protein-bound fraction serves as a reservoir, gradually releasing the drug as the free form is metabolized or excreted. 

Step 2: Pharmacodynamic and pharmacokinetic implications. 
- Pharmacodynamically inert: Since bound drugs cannot interact with receptors or target tissues, they are pharmacodynamically inactive.
 - Pharmacokinetically active: Plasma-bound drugs can influence drug distribution and half-life but are not inert in pharmacokinetic terms. 

Step 3: Why other options are incorrect. - (A) Pharmacodynamically active: Incorrect, as only free drugs interact with receptors. 
- (B) Pharmacokinetically inert: Incorrect, as binding affects drug distribution and elimination. 
- (C) Pharmacokinetically and pharmacodynamically inert: Incorrect, because plasma-bound drugs influence pharmacokinetics but not pharmacodynamics.