**Core Concept**
Chemical labyrinthectomy is a procedure used in the management of Meniere's disease, a disorder of the inner ear characterized by vertigo, tinnitus, hearing loss, and aural fullness. The transtympanic route involves the injection of a medication through the eardrum to selectively destroy the vestibular hair cells in the inner ear, thereby reducing the frequency and severity of vertigo attacks.

**Why the Correct Answer is Right**
Gentamicin, an aminoglycoside antibiotic, is used for chemical labyrinthectomy in Meniere's disease due to its ototoxic properties. When injected into the middle ear, gentamicin is absorbed by the vestibular hair cells, leading to their destruction and subsequent reduction in vestibular function. This results in decreased vertigo attacks and improved quality of life for the patient. The effectiveness of gentamicin in this procedure is attributed to its ability to bind to the 16S subunit of the bacterial ribosome, thereby inhibiting protein synthesis and leading to cell death.

**Why Each Wrong Option is Incorrect**
**Option A:** Amikacin is another aminoglycoside antibiotic, but it is not typically used for chemical labyrinthectomy due to its higher toxicity profile and less favorable ototoxic effects.
**Option C:** Amoxycillin is a broad-spectrum penicillin antibiotic used to treat a wide range of bacterial infections, but it is not ototoxic and therefore not suitable for chemical labyrinthectomy.
**Option D:** Cyclosporine is an immunosuppressive agent used to prevent rejection in organ transplant patients, but it is not ototoxic and has no role in the management of Meniere's disease.

**Clinical Pearl / High-Yield Fact**
When performing chemical labyrinthectomy, it is essential to use a precise and controlled delivery system to minimize the risk of intracochlear injection, which can lead to hearing loss and other complications. A thorough understanding of the anatomy of the inner ear and the ototoxic effects of gentamicin is crucial to ensure the success of this procedure.

**✓ Correct Answer: B. Gentamicin**