Which statement best describes the concentration-time plot for zero-order elimination?

Which statement best describes the concentration-time plot for zero-order elimination?

• A. Straight-line decline with constant slope
• B. Exponential decline
• C. Constant concentration over time
• D. Increasing concentration

Answer: (A)

In zero-order elimination, a constant amount of drug is removed per unit time, regardless of how much is present. Because the amount eliminated each minute is fixed, the concentration declines by the same amount in equal time intervals, yielding a straight-line decrease on a plot of concentration versus time. The slope is constant and negative, reflecting the constant rate of loss. This differs from first-order elimination, where the rate depends on concentration and the plot shows an exponential decline. The other options describe scenarios that don’t match zero-order behavior: a constant concentration implies no net loss (or ongoing input to maintain it), an increasing concentration means net input exceeding loss, and an exponential decline corresponds to first-order kinetics.

In zero-order elimination, a constant amount of drug is removed per unit time, regardless of how much is present. Because the amount eliminated each minute is fixed, the concentration declines by the same amount in equal time intervals, yielding a straight-line decrease on a plot of concentration versus time. The slope is constant and negative, reflecting the constant rate of loss. This differs from first-order elimination, where the rate depends on concentration and the plot shows an exponential decline. The other options describe scenarios that don’t match zero-order behavior: a constant concentration implies no net loss (or ongoing input to maintain it), an increasing concentration means net input exceeding loss, and an exponential decline corresponds to first-order kinetics.