A drug has a volume of distribution (Vd) of 700 L in a 70 kg patient. Which statement best explains this finding?

• A The drug is largely confined to the plasma compartment
• B The drug is extensively bound to plasma proteins
• C The drug is actively secreted into the renal tubule
• D The drug is highly lipophilic and distributes into deep tissue compartments ✓

Explanation

A Vd of 700 L is far greater than total body water (approximately 42 L) or plasma volume (approximately 3 L), indicating the drug extensively partitions into tissues. Highly lipophilic drugs and those with high tissue binding exhibit very large Vd values. Plasma-protein bound drugs actually have a smaller Vd because binding keeps drug in the vascular compartment. Renal secretion affects elimination, not distribution.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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