Most kinetic processes in the body follow which order of kinetics?

Most kinetic processes in the body follow which order of kinetics?

• A. Zero-order kinetics
• B. First-order kinetics
• C. Second-order kinetics
• D. Mixed-order kinetics

Answer: (B)

Most kinetic processes in the body follow first-order kinetics because, at typical drug concentrations, metabolic and elimination pathways are not saturated. When the substrate concentration is well below the enzyme’s Km, the rate of metabolism is proportional to concentration, so doubling the amount present roughly doubles the rate. As the drug is cleared and its concentration decreases, the rate declines proportionally, producing an exponential decline in drug level with a constant half-life. Zero-order kinetics would occur only when the metabolic capacity is saturated, giving a constant rate regardless of concentration. Second-order kinetics would depend on the product of two concentrations, which isn’t the usual pattern for single-substrate bodily processes. Mixed-order scenarios are special cases where the apparent order changes with concentration or involves multiple steps. Hence, first-order kinetics best describes the common behavior observed under normal physiological conditions.

Most kinetic processes in the body follow first-order kinetics because, at typical drug concentrations, metabolic and elimination pathways are not saturated. When the substrate concentration is well below the enzyme’s Km, the rate of metabolism is proportional to concentration, so doubling the amount present roughly doubles the rate. As the drug is cleared and its concentration decreases, the rate declines proportionally, producing an exponential decline in drug level with a constant half-life. Zero-order kinetics would occur only when the metabolic capacity is saturated, giving a constant rate regardless of concentration. Second-order kinetics would depend on the product of two concentrations, which isn’t the usual pattern for single-substrate bodily processes. Mixed-order scenarios are special cases where the apparent order changes with concentration or involves multiple steps. Hence, first-order kinetics best describes the common behavior observed under normal physiological conditions.