A drug has a volume of distribution (Vd) of 350 L and a plasma half-life of 20 hours. The total body clearance (CL) can be calculated as: CL = (0.693 × Vd) / t1/2. What is the clearance in mL/min?

• A 201 mL/min ✓
• B 100 mL/min
• C 200 mL/min
• D 300 mL/min

Explanation

Using CL = (0.693 × Vd) / t1/2: CL = (0.693 × 350,000 mL) / (20 × 60 min) = 242,550 / 1200 = 202.125 mL/min ≈ 201 mL/min (closest answer). The formula links the elimination rate constant (ke = 0.693/t1/2) to clearance via Vd. High Vd with moderate t1/2 yields substantial clearance, indicating extensive distribution into tissues with good elimination. This relationship is fundamental: CL = ke × Vd.

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

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