**Question:** An ototoxic drug which mainly affects the vestibular component is

A. Amphotericin B
B. Gentamicin
C. Vancomycin
D. Cisplatin

**Correct Answer:** B. Gentamicin

**Core Concept:** Ototoxicity is a side effect of certain medications that damages the inner ear structures, leading to hearing loss and vestibular dysfunction. The vestibular system is responsible for maintaining balance and spatial orientation. It is divided into the lateral (labyrinth) and medial vestibular systems, with the vestibulocochlear nerve (cranial nerve VIII) connecting them to the brain.

**Why the Correct Answer is Right:** Gentamicin is a type of aminoglycoside antibiotic that has a high affinity for the kidney's brush border, where it accumulates and causes nephrotoxicity. However, it also has a unique ability to cross the blood-labyrinth barrier, affecting the vestibular system. Its ototoxicity is primarily due to the inhibition of the enzymes in the cochlear and vestibular systems, particularly the mitochondrial enzyme complex I, which is responsible for oxidative phosphorylation. This inhibition results in the production of reactive oxygen species (ROS) and ultimately leads to cellular damage, causing hearing loss and vestibular dysfunction.

**Why Each Wrong Option is Incorrect:**

A. Amphotericin B: This antifungal drug is primarily nephrotoxic and neurotoxic, causing liver dysfunction and central nervous system (CNS) issues, respectively. It does not have a significant ototoxic effect on the vestibular system.

C. Vancomycin: This antibiotic primarily targets the bacterial cell wall synthesis, causing nephrotoxicity and ototoxicity. However, it mainly affects the cochlea (hearing) rather than the vestibular system.

D. Cisplatin: This chemotherapeutic agent is widely known for its nephrotoxicity and ototoxicity, affecting the cochlea causing hearing loss. Although it can affect the vestibular system, the focus is primarily on the cochlea, making B the correct answer.

**Clinical Pearl:** Ototoxicity is a significant concern with the use of aminoglycosides, particularly gentamicin. Clinicians should monitor patients for symptoms of hearing loss and vestibular dysfunction when prescribing these drugs, especially in patients with pre-existing kidney or ear disorders. Prompt intervention can help minimize the risk of permanent damage to these vital structures.