Zero order kinetics is followed by all of the following drugs EXCEPT:
**Core Concept**
Zero-order kinetics refers to a type of pharmacokinetic process where the rate of drug elimination is constant and independent of the drug's concentration. This phenomenon occurs when a drug is metabolized by a saturable enzyme, causing the rate of elimination to reach a maximum value regardless of the plasma concentration.
**Why the Correct Answer is Right**
In zero-order kinetics, the rate of drug elimination is not dependent on the drug's concentration. Instead, it is limited by the capacity of the enzyme or system responsible for metabolism. When a drug is metabolized by a saturable enzyme, the rate of elimination becomes constant and independent of the plasma concentration, leading to a flat plasma concentration-time profile. This is characteristic of drugs that are metabolized by enzymes with high Km values, such as ethanol and aspirin.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because, in zero-order kinetics, the rate of drug elimination is constant and independent of the drug's concentration. If the rate of elimination were directly proportional to the drug's concentration, it would follow first-order kinetics.
* **Option B:** This option is incorrect because, in zero-order kinetics, the plasma concentration-time profile is flat, and the rate of elimination is constant. If the drug's concentration affects its elimination rate, it would follow first-order kinetics.
* **Option C:** This option is incorrect because, in zero-order kinetics, the rate of drug elimination is limited by the capacity of the enzyme or system responsible for metabolism. If the drug's concentration affects its elimination rate, it would follow first-order kinetics.
**Clinical Pearl / High-Yield Fact**
Zero-order kinetics can occur with drugs that are metabolized by enzymes with high Km values, such as ethanol and aspirin. This phenomenon can lead to a flat plasma concentration-time profile, which may require adjustments in dosing frequency or administration.
**Correct Answer: D.**