Pharmacokinetics and Pharmacodynamics · USMLE Step 1

Which term refers to the fraction of drug unbound to plasma proteins and free to exert effect or be eliminated?

  1. Volume of distribution
  2. Bioavailability
  3. Clearance
  4. Free (unbound) fraction
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Correct answer: Free (unbound) fraction

Only the unbound fraction (free drug) is pharmacologically active and available for elimination. Protein-bound drug is generally inactive until released.

Difficulty: Medium Question 12 of 20

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