Which Anti-Tubercular drug damages the 8th cranial nerve?

Appeared in: AIIMS Delhi NO - 2017

Explanation

Streptomycin is an aminoglycoside antibiotic used in the treatment of drug-resistant tuberculosis.
A well-documented and serious side effect of Streptomycin is ototoxicity, which is direct damage to the 8th cranial nerve (vestibulocochlear nerve).
This toxicity can affect both branches of the nerve, leading to cochlear damage (hearing loss, tinnitus) and vestibular damage (vertigo, dizziness, loss of balance).
The damage is often dose-related and can be irreversible, making monitoring essential.

Option B: Ethambutol's primary neurotoxicity is optic neuritis, which is damage to the 2nd cranial (optic) nerve, not the 8th. This leads to symptoms like blurred vision, difficulty with color discrimination (especially red-green), and reduced visual acuity.
Option C: Isoniazid's most common neurotoxicity is peripheral neuropathy, characterized by numbness, tingling, and pain in the hands and feet. It does not typically cause damage to the 8th cranial nerve.
Option D: This option is incorrect because only Streptomycin among the choices is primarily responsible for damaging the 8th cranial nerve. Ethambutol and Isoniazid have different primary sites of neurotoxicity.

Clinical Relevance

Nursing practice connection: Knowing Adverse effects of anti-tubercular medications, specifically neurotoxicity helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must perform baseline and periodic assessments of hearing and balance for any patient receiving Streptomycin.
It is critical to educate patients to immediately report symptoms like ringing in the ears (tinnitus), dizziness (vertigo), or any hearing loss.
Early detection and reporting can help prevent permanent disability, as the provider may decide to adjust the dose or switch to an alternative medication.

How to Approach the Question

First, identify the key terms in the question: 'Anti-Tubercular drug' and '8th cranial nerve'.
The question asks for a specific adverse effect (damage to the 8th nerve, which controls hearing and balance) of a specific class of drugs.
Systematically review the known major side effects of each option.
Recall or deduce that Streptomycin is an aminoglycoside, a class famous for ototoxicity (8th nerve damage) and nephrotoxicity.
Recall that Ethambutol's key side effect is optic neuritis (2nd nerve damage), often remembered by the 'E' in Ethambutol for 'Eye'.
Recall that Isoniazid's key side effect is peripheral neuropathy.

Concept Tested & Keywords

Concept Tested: Adverse effects of anti-tubercular medications, specifically neurotoxicity.
Stem keywords: Anti-Tubercular drug, 8th cranial nerve, damages
Lead-in keywords: Which

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E6 Medicine Harrison 22e Part 1 p. 1467-1469

E6 Pharmacology Katzung 16e p. 1319-1321

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 1836-1838

Practise the full AIIMS Delhi NO - 2017

Attempt every question from this paper in a timed mock, then review the full solution for each one.