A drug has a volume of distribution (Vd) of 200 L in a 70-kg adult. Which statement about this drug is most likely correct?
- A The drug has extensive tissue binding or accumulates in body fat, with low plasma concentrations relative to total body drug ✓
- B The drug is primarily confined to the plasma compartment with minimal tissue binding
- C The drug is a large hydrophilic molecule that cannot cross capillary membranes
- D The drug undergoes zero-order kinetics due to its large volume of distribution
Explanation
Volume of distribution (Vd) is a conceptual pharmacokinetic parameter representing the apparent volume needed to contain the total body drug at the observed plasma concentration. A Vd of 200 L (nearly 3× total body water of ~42 L) indicates extensive drug distribution and sequestration in peripheral tissues, fat depots, or intracellular compartments, with only a small fraction remaining in plasma. Drugs confined to plasma have Vd approximately equal to plasma volume (~4–5 L); large Vd values reflect lipophilicity or high tissue binding, not high plasma concentrations.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.