## **Core Concept**
The question tests the understanding of drug metabolism, specifically the process of acetylation. Acetylation is a phase II metabolic reaction where an acetyl group is introduced to a molecule, often making it more water-soluble and easier to excrete. This process is crucial for metabolizing certain drugs.

## **Why the Correct Answer is Right**
Isoniazid and Hydralazine are classic examples of drugs metabolized by acetylation. This process involves the transfer of an acetyl group from acetyl-CoA to the drug, typically catalyzed by the enzyme **N-acetyltransferase (NAT)**. This reaction is significant for these drugs as it affects their plasma half-life and susceptibility to inducing side effects like drug-induced lupus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Isoniazid is indeed metabolized by acetylation. This is a well-known fact and a key aspect of its pharmacokinetics, influencing its dosing and side effect profile.
- **Option B:** Hydralazine is also metabolized by acetylation. The rate of acetylation can affect the drug's efficacy and toxicity.
- **Option D:** Procainamide is another drug whose metabolite, N-acetylprocainamide (NAPA), is produced through acetylation. Both the parent drug and its metabolite have pharmacological activity.

## **Clinical Pearl / High-Yield Fact**
A critical clinical pearl is that the rate of acetylation can vary among individuals, categorizing them as either "fast acetylators" or "slow acetylators." This variation affects the plasma levels and, consequently, the efficacy and toxicity of drugs metabolized by acetylation. For instance, slow acetylators are at a higher risk of developing drug-induced lupus when taking Hydralazine or Procainamide.

## **Correct Answer:** .