A drug has Vd = 50 L in a 70 kg patient. What is Vd in L/kg and what does this imply about tissue distribution?

• A. 0.71 L/kg; moderate tissue distribution beyond plasma but not extremely lipophilic
• B. 1.0 L/kg; extensive tissue distribution
• C. 0.1 L/kg; confined to plasma
• D. 2.0 L/kg; very high tissue distribution

Answer: (A)

Volume of distribution per kilogram shows how widely a drug spreads beyond plasma into body tissues. Compute it by dividing the total Vd by body weight: 50 L / 70 kg ≈ 0.71 L/kg. This value sits above plasma volume and extracellular fluid but well below full tissue-fat distribution, indicating moderate tissue distribution beyond plasma without being extremely lipophilic. If it were around 0.1 L/kg, the drug would be confined to plasma; around 1 L/kg suggests more extensive tissue distribution; and about 2 L/kg or higher would indicate very high tissue distribution.