Pharmacokinetics and Pharmacodynamics · USMLE Step 1

Which pharmacokinetic concept explains why loading doses are used when a drug has long half-life and slow accumulation to steady state?

  1. Clearance
  2. Volume of distribution
  3. First-pass metabolism
  4. Pharmacodynamics
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Correct answer: Volume of distribution

When Vd is large or half-life is long, drug accumulates slowly; a loading dose based on Vd rapidly achieves therapeutic concentrations before maintenance dosing.

Difficulty: Medium Question 19 of 20

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