**Core Concept**
In pharmacokinetics, first-order kinetics describes the elimination of a drug that is directly proportional to its plasma concentration. This means that the rate of elimination remains constant, regardless of the initial dose or concentration of the drug.

**Why the Correct Answer is Right**
The elimination of a drug after four half-lives in first-order kinetics can be calculated using the formula: 100% - (1/2)^n, where n is the number of half-lives. After four half-lives, the fraction of the drug remaining is (1/2)^4 = 1/16, which is equivalent to 6.25%. Therefore, 93.75% of the drug is eliminated after four half-lives.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the concept of half-lives in first-order kinetics. The elimination of a drug after four half-lives cannot be determined by simply dividing the initial dose by four.

* **Option B:** This option is incorrect because it is based on second-order kinetics, where the rate of elimination is proportional to both the concentration of the drug and another factor, such as the concentration of a binding protein.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that in first-order kinetics, the rate of elimination remains constant, and the half-life of the drug is independent of the initial dose. This concept is crucial in understanding the pharmacokinetics of various drugs.

**Correct Answer: C. 93.75%**