Which first-line anti-TB drug is contraindicated for a pregnant woman?

Appeared in: RML PRE 2025

Explanation

Streptomycin is an aminoglycoside antibiotic, a class of drugs known for potential toxicity.
It is strictly contraindicated in pregnancy because it crosses the placenta.
The primary risk to the fetus is ototoxicity, which can cause irreversible damage to the 8th cranial nerve, leading to congenital deafness.
Streptomycin can also cause nephrotoxicity (kidney damage) in the developing fetus.

Option B: Isoniazid is a first-line anti-TB drug that is considered safe and is recommended for use during pregnancy.
Option C: Ethambutol is considered safe to use during pregnancy and is part of the standard first-line treatment.
Option D: Pyrazinamide is recommended by the World Health Organization (WHO) for treating TB in pregnant women, as the benefits of treating the disease are considered greater than the potential risks.

Clinical Relevance

Nursing practice connection: Use the key finding related to Contraindications of anti-tuberculosis drugs during pregnancy to guide bedside assessment, documentation, and the next nursing action.
Treating tuberculosis in pregnancy is critical, as untreated TB poses a much greater risk to the mother and fetus than the treatment itself. The goal is to use effective drugs that are safe for the fetus.
A key nursing intervention is to ensure any pregnant patient on Isoniazid also receives pyridoxine (Vitamin B6) supplementation to prevent peripheral neuropathy.
Nurses must monitor for adverse effects of all TB drugs, such as hepatotoxicity from Isoniazid, Rifampicin, and Pyrazinamide, through regular liver function tests.

How to Approach the Question

First, identify the core of the question: it asks for a first-line anti-TB drug that is UNSAFE ('contraindicated') in pregnancy.
Recall the common first-line anti-TB drugs, often remembered by the mnemonic RIPE(S): Rifampicin, Isoniazid, Pyrazinamide, Ethambutol, and Streptomycin.
Systematically review the safety profile of each drug in pregnancy.
Remember that aminoglycosides, like Streptomycin, are generally avoided in pregnancy due to known fetal risks.
Specifically, recall or deduce that Streptomycin's major toxicity is damage to the 8th cranial nerve (ototoxicity), which would be devastating to a developing fetus.
Confirm that the other drugs (Isoniazid, Ethambutol, Pyrazinamide) are generally considered safe, making Streptomycin the correct answer.

Concept Tested & Keywords

Concept Tested: Contraindications of anti-tuberculosis drugs during pregnancy
Stem keywords: first-line anti-TB drug, contraindicated, pregnant woman
Lead-in keywords: Which
Clinical cues: Age/sex group narrows the expected diagnosis, intervention, or normal reference range.
Negative lead-in flag: false

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E6 Pharmacology Katzung 16e p. 1319-1321

E6 Medicine Harrison 22e Part 1 pp. 1464-1466, 1467-1469

Practise the full RML PRE 2025

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