Learning Objective

Understand the concept of zero-order drug elimination, its kinetic characteristics, and the clinical examples where it occurs.

Zero-Order Elimination Rate

Zero-order elimination occurs when a constant amount of drug is eliminated per unit time, regardless of plasma concentration.

Key Points:

• The rate of elimination is independent of plasma concentration.
• No fixed half-life (t₁/₂): Half-life varies with plasma concentration.
• Clinical examples:
  • Ethanol (except at very low blood levels)
  • Phenytoin (high therapeutic doses)
  • Aspirin (toxic doses)

Example:

• Dose: 80 mg
• Elimination: 10 mg every 4 hours
• Interpretation: 10 mg removed every 4 h, independent of remaining plasma concentration.

Activity