A high volume of distribution indicates what about drug distribution?

• A. Confined to intravascular space
• B. Reaches interstitial tissue and intracellular compartments
• C. Remains mostly in plasma
• D. Is limited to extracellular fluid

Answer: (B)

Volume of distribution shows how widely a drug spreads beyond the blood. A high Vd means the drug leaves the bloodstream and distributes widely into body tissues, reaching interstitial spaces and even intracellular compartments. This happens when the drug is lipophilic, binds to tissues, or crosses membranes readily, so plasma concentrations are relatively low for a given amount in the body. Hence, high Vd indicates extensive distribution into tissues and cells.

If a drug were confined to the intravascular space or remained mostly in plasma, the distribution would be limited and the Vd would be small. Being limited to extracellular fluid would also reflect a more restricted distribution, not a high Vd.