If a drug does not have concentration-dependent killing, how will the dose-response curve look and what type of kinetics characterize it?

• A. Plateau curve. Second-order kinetics.
• B. Upward curve. First-order kinetics.
• C. Horizontal line. Zero-order kinetics.
• D. Steep incline. Mixed-order kinetics.

Answer: (C)

Concentration-dependent killing means the drug’s effect grows with higher concentrations. If that isn’t the case, increasing the dose won’t yield a greater effect, so the dose–response relationship becomes a flat line—the same effect regardless of dose within the tested range. The kinetics described is zero-order, where the body eliminates a constant amount of drug per unit time, independent of how much is present, typically because elimination pathways are saturated. So a drug with no concentration-dependent killing tends to show a horizontal dose–response together with zero-order elimination.