If a drug distributes extensively into body tissues, what can be inferred about its volume of distribution?

If a drug distributes extensively into body tissues, what can be inferred about its volume of distribution?

• A. It is small
• B. It is large
• C. It is zero
• D. It is negligible

Answer: (B)

When a drug distributes extensively into body tissues, the volume of distribution is large. Vd is a theoretical volume that relates the total amount of drug in the body to the plasma concentration. If most of the drug moves into tissues, the plasma concentration for a given total amount is low, which makes the calculated Vd large. Conversely, drugs that stay mostly in the plasma have a small Vd. So the best inference here is that the volume of distribution is large.

When a drug distributes extensively into body tissues, the volume of distribution is large. Vd is a theoretical volume that relates the total amount of drug in the body to the plasma concentration. If most of the drug moves into tissues, the plasma concentration for a given total amount is low, which makes the calculated Vd large. Conversely, drugs that stay mostly in the plasma have a small Vd. So the best inference here is that the volume of distribution is large.