Which statement best describes Zero-Order Elimination Kinetics?

Which statement best describes Zero-Order Elimination Kinetics?

• A. The rate of elimination is proportional to the concentration.
• B. A steady and constant rate of elimination regardless of concentration.
• C. Elimination only occurs in the presence of active metabolism.
• D. Elimination is negligible at steady state.

Answer: (B)

Zero-order elimination means the body removes a constant amount of drug per unit time, regardless of how much drug is present. This happens when the metabolizing enzymes or transport systems are saturated, so increasing the concentration doesn’t speed up clearance. As a result, the elimination rate stays steady and the drug concentration falls linearly over time. This is different from first-order kinetics, where the rate depends on concentration (higher levels are cleared faster). The other statements don’t fit because zero-order elimination isn’t about needing active metabolism, nor is elimination negligible at steady state—the rate remains constant, not zero.

Zero-order elimination means the body removes a constant amount of drug per unit time, regardless of how much drug is present. This happens when the metabolizing enzymes or transport systems are saturated, so increasing the concentration doesn’t speed up clearance. As a result, the elimination rate stays steady and the drug concentration falls linearly over time. This is different from first-order kinetics, where the rate depends on concentration (higher levels are cleared faster). The other statements don’t fit because zero-order elimination isn’t about needing active metabolism, nor is elimination negligible at steady state—the rate remains constant, not zero.