A drug is administered as a 600 mg IV bolus. At time zero, the plasma concentration measured by back-extrapolation is 12 mg/L. The volume of distribution (Vd) of this drug is:

• A 7200 L
• B 50 L ✓
• C 72 L
• D 7.2 L

Explanation

Volume of distribution (Vd) = Dose / C0 = 600 mg / 12 mg/L = 50 L. A Vd of 50 L is consistent with moderate tissue distribution (slightly exceeding total body water of ~42 L), suggesting some tissue binding but no extensive sequestration. Drugs with Vd > 500 L (e.g., chloroquine) indicate massive tissue accumulation. The other options do not satisfy the equation: 600/12 = 50, not 7200, 72 or 7.2.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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