Zero order kinetics is independent of:
**Core Concept**
Zero order kinetics is a type of pharmacokinetic process where the rate of drug elimination is constant and independent of the drug concentration. This is in contrast to first-order kinetics, where the rate of elimination is directly proportional to the drug concentration. Zero order kinetics is often seen with drugs that are metabolized by a saturable enzyme.
**Why the Correct Answer is Right**
The correct answer is the factor that does not affect the rate of drug elimination in zero order kinetics. In zero order kinetics, the rate of elimination is constant and is not dependent on the concentration of the drug. This is because the enzyme responsible for metabolizing the drug is saturated, and the rate of elimination is determined by the rate at which the enzyme can metabolize the drug, rather than the amount of drug available. As a result, the rate of elimination is independent of the drug concentration.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because the rate of elimination in zero order kinetics is actually dependent on the amount of drug available. If the amount of drug available increases, the rate of elimination will also increase, even though the rate of elimination is constant.
**Option B:**
This option is incorrect because the rate of elimination in zero order kinetics is actually dependent on the enzyme that is responsible for metabolizing the drug. If the enzyme is saturated, the rate of elimination will be constant and independent of the drug concentration.
**Option C:**
This option is incorrect because the rate of elimination in zero order kinetics is actually dependent on the pH of the body fluids. If the pH changes, the rate of elimination may change, even though the rate of elimination is constant.
**Clinical Pearl / High-Yield Fact**
Zero order kinetics is often seen with drugs that are metabolized by a saturable enzyme, such as ethanol and certain barbiturates. This can lead to non-linear pharmacokinetics, where small changes in dose can result in large changes in drug concentration.
**Correct Answer: B. Enzyme. Enzyme saturation leads to zero order kinetics.**