A drug has a volume of distribution (Vd) of 350 L and a clearance of 35 L/h. Calculate its elimination half-life.
- A 5 hours
- B 6.93 hours ✓
- C 10 hours
- D 14 hours
Correct answer: B. 6.93 hours
Explanation
t½ = 0.693 × Vd / CL = 0.693 × 350 L / 35 L/h = 0.693 × 10 h = 6.93 hours. This confirms that half-life is proportional to volume of distribution and inversely proportional to clearance. A large Vd (extensive tissue binding) prolongs half-life even if clearance is reasonable. For clinical context, it would take approximately 5 half-lives (~34.65 h) to reach steady state and to wash out the drug after cessation.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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