Which statement best describes First-Order Elimination Kinetics?

Which statement best describes First-Order Elimination Kinetics?

• A. The rate of elimination is proportional to the concentration of the drug.
• B. The rate of elimination is constant regardless of concentration.
• C. Elimination occurs only at high concentrations.
• D. Elimination rate decreases with time.

Answer: (A)

First-order elimination kinetics means the body's removal of a drug happens at a rate that is proportional to how much drug is in the body. In other words, the more drug present, the faster it’s eliminated, and as the concentration falls, the elimination rate falls too. This is described by rate = k × C, where k is the constant and C is the concentration. The consequence is exponential decay and a constant half-life, meaning the same proportion of drug is cleared in each unit of time regardless of the starting amount. This is different from zero-order kinetics, where a constant amount is eliminated per unit time regardless of concentration. The idea that elimination occurs only at high concentrations or that the rate simply decreases with time without tying to the actual concentration aren’t accurate descriptions of first-order kinetics.

First-order elimination kinetics means the body's removal of a drug happens at a rate that is proportional to how much drug is in the body. In other words, the more drug present, the faster it’s eliminated, and as the concentration falls, the elimination rate falls too. This is described by rate = k × C, where k is the constant and C is the concentration. The consequence is exponential decay and a constant half-life, meaning the same proportion of drug is cleared in each unit of time regardless of the starting amount.

This is different from zero-order kinetics, where a constant amount is eliminated per unit time regardless of concentration. The idea that elimination occurs only at high concentrations or that the rate simply decreases with time without tying to the actual concentration aren’t accurate descriptions of first-order kinetics.