A drug follows first-order elimination kinetics. Which statement best characterizes this process?
- A A constant fraction of drug is eliminated per unit time ✓
- B The elimination rate is independent of plasma concentration
- C A constant amount of drug is eliminated per unit time
- D The elimination half-life increases as the dose increases
Correct answer: A. A constant fraction of drug is eliminated per unit time
Explanation
First-order kinetics means a constant fraction of drug is eliminated per unit time, making the elimination rate proportional to plasma concentration. Zero-order kinetics eliminates a constant amount per unit time. In first-order kinetics, half-life is constant and independent of dose. Zero-order kinetics shows dose-dependent half-life changes, as seen with phenytoin at therapeutic concentrations.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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