Final answer:
The correct option is 'a) Refers to drug elimination with a constant half-life', since a first-order reaction is characterized by a constant half-life that is independent of the reactant's concentration, represented by the equation t₁/₂ = 0.693/k.
Step-by-step explanation:
First-order kinetics in terms of drug elimination typically refers to the process where the drug's half-life is constant and the rate of elimination is proportional to the drug's concentration at that time. This means that as the concentration of the drug decreases, so does the rate of elimination. The half-life of a first-order reaction is independent of the initial concentration, which is mathematically represented by the equation t₁/₂ = 0.693/k, where k is the rate constant.
In contrast, zero-order reactions have a half-life that varies with concentration, as demonstrated by the equation [A] = -kt + [A]o. Meanwhile, for second-order reactions, the half-life is also dependent on the initial concentration. These distinctions are crucial in pharmacokinetics for understanding how different drugs are metabolized and cleared from the body.