Which of the following is NOT a hepatotoxic antitubercular drug?

Appeared in: NIMHANS Nursing Officer - 2021

Explanation

Ethambutol is the correct choice as it is not considered a primary hepatotoxic drug among the first-line antitubercular agents.
Its most significant, dose-related adverse effect is optic neuritis, which affects vision.
While other anti-TB drugs require regular liver function monitoring, the key monitoring parameter for Ethambutol is visual acuity and color vision testing.

Option A: Pyrazinamide is incorrect because it is considered the most hepatotoxic of the first-line anti-TB drugs.
Option B: Rifampicin is incorrect because it is a well-known cause of drug-induced hepatitis and also causes a characteristic orange discoloration of body fluids.
Option C: Isoniazid is incorrect because it can cause hepatitis. The risk is increased in older patients and those who consume alcohol.

Clinical Relevance

Nursing practice connection: Knowing Adverse effects of antitubercular medications helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must monitor liver function tests (AST, ALT) before and during treatment for patients on Isoniazid, Rifampicin, and Pyrazinamide, and educate them to report signs of hepatitis (jaundice, nausea, dark urine).
For patients on Ethambutol, the nursing priority shifts to monitoring vision. Baseline and monthly visual acuity and color vision tests are crucial.
What if? If a patient on a standard RIPE regimen (Rifampicin, Isoniazid, Pyrazinamide, Ethambutol) develops jaundice and has AST levels 5 times the upper limit of normal, the hepatotoxic drugs (INH, RIF, PZA) must be stopped immediately, while Ethambutol may be continued with a modified regimen pending further investigation.

How to Approach the Question

First, identify the core of the question: it asks to find the anti-TB drug that does NOT cause liver damage (hepatotoxicity).
The keyword 'NOT' is critical. This means three options are hepatotoxic, and one is not.
Recall the major side effects of the four main first-line anti-TB drugs: Isoniazid (INH), Rifampicin (RIF), Pyrazinamide (PZA), and Ethambutol (EMB).
Systematically review each option based on its primary toxicity:
Pyrazinamide: Known for hepatotoxicity and hyperuricemia.
Rifampicin: Known for hepatotoxicity and orange body fluids.

Concept Tested & Keywords

Concept Tested: Adverse effects of antitubercular medications
Stem keywords: hepatotoxic, antitubercular drug
Lead-in keywords: NOT
Negative lead-in flag: This question uses negative framing ('NOT'), asking you to identify the exception among the options.

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E6 Medicine Harrison 22e Part 1 p. 1464-1466

E6 Pharmacology Katzung 16e p. 1315-1317

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