Zero-Order Kinetics — FRCA Primary MCQ
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Correct answer: D — A constant amount of drug is eliminated per unit time
Explanation lettering: B = shown as A · D = shown as B · E = shown as C · A = shown as D · C = shown as E
A is correct. During zero-order elimination, a constant amount of drug is removed per unit time because the relevant elimination pathway is operating at a concentration-independent, usually saturated, rate. Consequently, drug amount and, for a fixed volume of distribution, plasma concentration decline linearly with time. Options B and C describe first-order elimination, in which a constant fraction is removed and elimination rate is proportional to concentration. The resulting concentration-time curve is exponential, so E also describes first-order kinetics. D is incorrect because zero-order kinetics do not have a concentration-independent half-life: the time required to halve the concentration increases as the starting concentration increases.
Reference: Denault D, Patel P, Ashurst JV. Physiology, Zero- and First-Order Kinetics. StatPearls, updated 10 January 2026. https://pubmed.ncbi.nlm.nih.gov/29763041/