If a drug X has a Vd of 1 L/kg in a 60 kg adult, what is the expected total Vd and where would it predominantly be?

If a drug X has a Vd of 1 L/kg in a 60 kg adult, what is the expected total Vd and where would it predominantly be?

• A. 60 L; predominantly Intracellular
• B. 60 L; predominantly intravascular
• C. 60 L; distributed uniformly
• D. 20 L; predominantly extracellular

Answer: (A)

Volume of distribution shows how widely a drug spreads beyond the bloodstream. If a drug has a Vd of 1 L/kg in a 60 kg adult, the total Vd is 60 L. To interpret the location, compare this with typical body fluid compartments: intravascular (plasma) ~4–5 L, extracellular fluids ~20 L, and total body water around 36 L in a person of this size. A Vd of 60 L exceeds all these fluid compartments, so most of the drug must be residing in tissues and cells rather than just in the blood or extracellular space. This pattern points to predominant intracellular distribution.

Volume of distribution shows how widely a drug spreads beyond the bloodstream. If a drug has a Vd of 1 L/kg in a 60 kg adult, the total Vd is 60 L. To interpret the location, compare this with typical body fluid compartments: intravascular (plasma) ~4–5 L, extracellular fluids ~20 L, and total body water around 36 L in a person of this size. A Vd of 60 L exceeds all these fluid compartments, so most of the drug must be residing in tissues and cells rather than just in the blood or extracellular space. This pattern points to predominant intracellular distribution.