Pharmaceutics Drug Disposition Practice Test

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 elimination process is saturated, so capacity limits the rate rather than concentration. Because the rate is fixed, it does not rise as concentration increases, and the concentration declines linearly over time until the drug is depleted. That’s why the statement describing the rate as constant and independent of concentration is the best fit. In zero-order kinetics, half-life is not constant across concentrations, since the amount removed per unit time is fixed. The idea that the rate increases with concentration is incorrect because the rate does not depend on concentration. While clearance would appear to increase over time as concentration falls (rate constant but concentration decreasing), the defining feature examiners focus on is the constant elimination rate itself.