For zero-order kinetics, which graph shows a straight line as drug concentration changes over time?

For zero-order kinetics, which graph shows a straight line as drug concentration changes over time?

• A. Concentration versus time (linear scale)
• B. Log concentration versus time
• C. Dose versus time
• D. Time versus dose

Answer: (A)

Zero-order kinetics means the drug is eliminated at a constant amount per unit time, independent of how much is present. Because of this constant removal rate, the concentration declines linearly with time: C = C0 − k0 t. Plotting concentration versus time on a linear axis therefore yields a straight line with slope −k0. If you use a logarithmic concentration plot, zero-order behavior doesn’t produce a straight line (that pattern is characteristic of first-order kinetics, where log C versus time is linear). Plotting dose versus time or time versus dose doesn’t reflect the constant-rate elimination in the same direct way. So the straight-line graph is concentration versus time on a linear scale.

Zero-order kinetics means the drug is eliminated at a constant amount per unit time, independent of how much is present. Because of this constant removal rate, the concentration declines linearly with time: C = C0 − k0 t. Plotting concentration versus time on a linear axis therefore yields a straight line with slope −k0. If you use a logarithmic concentration plot, zero-order behavior doesn’t produce a straight line (that pattern is characteristic of first-order kinetics, where log C versus time is linear). Plotting dose versus time or time versus dose doesn’t reflect the constant-rate elimination in the same direct way. So the straight-line graph is concentration versus time on a linear scale.