Which of the following best describes the relationship between plasma protein binding and drug distribution volume (Vd)?

Question

Accepted Answer

B. High protein binding decreases Vd because the drug remains in the vascular compartment. ## Plasma Protein Binding and Distribution Volume

**Key Point:** Plasma protein binding is **inversely related** to volume of distribution (Vd).

### Mechanism:
- When a drug is highly bound to plasma proteins (albumin, α1-acid glycoprotein), it remains sequestered in the vascular compartment
- The bound drug cannot freely distribute into tissues
- This results in a **smaller apparent Vd** (drug appears confined to plasma)
- Conversely, drugs with low protein binding distribute more freely into tissues, yielding larger Vd values

### Clinical Pearl:
- Highly protein-bound drugs (e.g., warfarin ~99%, diazepam ~99%) have Vd ≈ plasma volume (3–5 L)
- Lipophilic, poorly protein-bound drugs (e.g., chloroquine) have Vd > 100 L

**High-Yield:** Remember: **Bound = Confined to plasma = Low Vd**

Answer

A. High protein binding increases Vd by preventing renal filtration

Answer

C. Protein binding has no effect on Vd; only lipophilicity matters

Answer

D. High protein binding increases Vd by enhancing tissue penetration

Which of the following best describes the relationship between plasma protein binding and drug distribution volume (Vd)?

Explanation

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