Zero-order kinetics is best described as:

• A. The rate of elimination is proportional to the drug concentration.
• B. The elimination rate is independent of drug concentration due to saturable metabolism.
• C. The half-life remains constant as dose increases.
• D. The clearance decreases as concentration increases.

Answer: (B)

Zero-order kinetics happens when the body's drug-metabolizing capacity is saturated. Once enzymes or pathways reach their maximum rate, they can’t eliminate more drug per unit time even if the concentration rises. So the elimination rate stays constant regardless of how much drug is present. This means higher doses push more drug through the same fixed elimination step, leading to higher plasma levels and a longer apparent half-life as dose increases. The key point is that the rate of elimination becomes independent of concentration because metabolism is saturated.

That’s why the best description is that the elimination rate is independent of drug concentration due to saturable metabolism.