## Core Concept
The question tests the knowledge of cytochrome P450 (CYP) enzymes, specifically CYP2D6, and its role in drug metabolism. CYP2D6 is one of the major enzymes involved in the metabolism of many drugs. It is a member of the cytochrome P450 superfamily, which plays a crucial role in the oxidative metabolism of many drugs.

## Why the Correct Answer is Right
The correct answer, , is metabolized by CYP2D6. This enzyme is particularly important for drugs that are substrates for it because it can significantly affect their plasma levels and, consequently, their efficacy and toxicity. Drugs metabolized by CYP2D6 can be affected by genetic polymorphisms that lead to poor, intermediate, extensive, or ultrarapid metabolizer phenotypes.

## Why Each Wrong Option is Incorrect
**Option A:** is not primarily metabolized by CYP2D6. Its metabolism involves other CYP enzymes.

**Option B:** is also not primarily metabolized by CYP2D6. It undergoes metabolism by different CYP enzymes.

**Option C:** This option might seem plausible but is incorrect because is not the best example of a drug metabolized by CYP2D6 compared to the correct answer.

## Clinical Pearl / High-Yield Fact
A key point to remember is that genetic variations in CYP2D6 can significantly affect the metabolism of drugs that are substrates for this enzyme. For example, codeine is a prodrug that requires conversion to morphine by CYP2D6 to produce analgesia. Poor metabolizers may experience reduced analgesia, while ultrarapid metabolizers may experience increased toxicity.

## Correct Answer Line
**Correct Answer: D. **