MDC Pharmacokinetics (PK) I Practice Exam

If Vd = 50 L and CL = 5 L/h, what is the half-life t1/2?

1.2 h 4.5 h 6.93 h 12 h

Correct Answer:

6.93 h

Explanation:

The half-life in first-order elimination is determined by t1/2 = 0.693 × Vd / CL. This ties how far the drug distributes (Vd) to how quickly it’s cleared (CL). Plugging in Vd = 50 L and CL = 5 L/h gives Vd/CL = 50/5 = 10 h. Multiply by 0.693 to get t1/2 = 6.93 h. So the half-life is about 6.93 hours. The other numbers would require different Vd/CL ratios (for example, a much smaller ratio would yield a shorter t1/2, and a larger ratio would yield a longer t1/2).

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