A drug has a volume of distribution of 40 L, a clearance of 10 L/h, and is administered as an IV bolus of 200 mg. What is its elimination half-life?

• A 2.8 hours ✓
• B 1.4 hours
• C 4.0 hours
• D 5.5 hours

Explanation

Half-life = 0.693 × Vd / CL = 0.693 × 40 L / 10 L/h = 0.693 × 4 h = 2.77 h ≈ 2.8 hours. The dose (200 mg) is not needed for half-life calculation; it determines initial plasma concentration (Co = Dose/Vd = 5 mg/L). This relationship shows that t½ is determined by distribution (Vd) and elimination (CL) independently of dose.

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

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