Zero-order kinetics occur in the following drug with high dose
**Core Concept**
Zero-order kinetics is a type of pharmacokinetic behavior where the rate of drug elimination is constant and independent of the drug concentration. This phenomenon is often observed with drugs that are eliminated by a saturable metabolic pathway, where the enzyme responsible for metabolism becomes saturated at high doses, leading to a constant rate of elimination.
**Why the Correct Answer is Right**
At high doses, the enzyme responsible for metabolism, such as cytochrome P450, becomes saturated. As a result, the rate of metabolism remains constant, regardless of the increase in drug concentration. This leads to a characteristic plateau in plasma concentration, where the rate of elimination is no longer dependent on the concentration of the drug. This phenomenon is observed with drugs that are primarily metabolized by a single enzyme or pathway, such as phenytoin.
**Why Each Wrong Option is Incorrect**
**Option A:** This drug is primarily metabolized by a first-order process, where the rate of elimination is directly proportional to the concentration of the drug.
**Option B:** This drug is eliminated primarily by renal excretion, which is a first-order process.
**Option C:** This drug is metabolized by multiple enzymes, which prevents the saturation of a single enzyme and maintains first-order kinetics.
**Clinical Pearl / High-Yield Fact**
Drugs that exhibit zero-order kinetics often have a narrow therapeutic index, making it essential to monitor plasma concentrations closely to avoid toxicity.
**Correct Answer:** C.