**Core Concept**
Phenytoin is an antiepileptic medication that works by blocking voltage-gated sodium channels, which reduces the frequency of action potentials in neurons, thereby reducing the excitability of the nervous system. It is a member of the hydantoin class of antiepileptic drugs.

**Why the Correct Answer is Right**
The side effects of phenytoin are primarily due to its effects on the central nervous system, cardiovascular system, and other bodily systems. At therapeutic doses, phenytoin can cause dizziness, ataxia, and nystagmus due to its depressant effects on the central nervous system. Additionally, phenytoin can cause gingival hyperplasia, hirsutism, and osteomalacia due to its effects on vitamin D metabolism and calcium absorption. **Phenytoin is also known to cause "purple glove syndrome" due to its effects on the peripheral nerves**.

**Why Each Wrong Option is Incorrect**
* **Option A:** While phenytoin can cause a range of side effects, it is not primarily known for causing hepatotoxicity like some other antiepileptic medications.
* **Option B:** Phenytoin is not typically associated with the development of diabetes mellitus.
* **Option C:** While phenytoin can cause a range of cardiovascular side effects, it is not primarily known for causing orthostatic hypotension.

**Clinical Pearl / High-Yield Fact**
* **Gingival hyperplasia is a common side effect of phenytoin, and it is often treated with good oral hygiene and regular dental check-ups**.

**Correct Answer: C.**