Veterinary Pharmacology Drugs Practice Test

Which statement about the relationship between half-life, volume of distribution, and clearance is correct?

t1/2 is independent of Vd and CL. t1/2 increases as CL increases. t1/2 is proportional to Vd and inversely proportional to CL. t1/2 depends on dose.

Correct Answer:

t1/2 is proportional to Vd and inversely proportional to CL.

Explanation:

The key idea is how half-life relates to distribution and clearance in first-order kinetics. The elimination rate constant k equals clearance divided by volume of distribution (k = CL / Vd), and the half-life t1/2 equals 0.693 divided by k. Rewriting gives t1/2 = 0.693 × Vd / CL. So, t1/2 increases with a larger volume of distribution and decreases with higher clearance. Dose generally doesn’t affect t1/2 in linear kinetics, so it’s not dependent on dose. That’s why the statement that half-life is proportional to Vd and inversely proportional to CL is the correct description.

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