INH (Isoniazid) is antagonist of which vitamin?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Pharmacology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Explanation

Isoniazid (INH), a primary antitubercular drug, is a direct antagonist of Vitamin B6 (pyridoxine).
The drug increases the urinary excretion of pyridoxine and also inhibits its conversion into the biologically active form, pyridoxal phosphate.
This interference with Vitamin B6 metabolism is the direct cause of peripheral neuropathy, a common dose-dependent side effect of INH.
To prevent this neurotoxicity, prophylactic supplementation with pyridoxine (10-50 mg/day) is a standard of care for patients on INH therapy.

Option A: Vitamin B5 (Pantothenic acid) is involved in the synthesis of coenzyme A and is not known to be antagonized by Isoniazid.
Option B: While INH has a structural similarity to Niacin (Vitamin B3) and can rarely cause pellagra-like symptoms, its primary and most clinically significant antagonism is with Vitamin B6.
Option D: Isoniazid does not interfere with the absorption or metabolism of Vitamin B12 (Cobalamin).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology: Drug-Vitamin Antagonism as background academic context rather than a clinical decision trigger.
Nurses must ensure that patients prescribed Isoniazid, especially those in high-risk groups (e.g., alcoholics, malnourished, diabetics, pregnant women), receive and take their concurrent pyridoxine supplement to prevent nerve damage.
A key nursing assessment for patients on INH is to regularly ask about and document any signs of peripheral neuropathy, such as tingling, numbness, or burning in the hands and feet, and report them to the provider.
What if? If a patient on INH therapy develops symptoms of peripheral neuropathy despite taking a standard prophylactic dose of pyridoxine (10 mg/day), the nurse should anticipate an order to increase the pyridoxine dosage to a therapeutic level, often 50-100 mg/day.

How to Approach the Question

First, identify the key terms in the question: 'Isoniazid (INH)' and 'antagonist of which vitamin'. This is a direct factual recall question from pharmacology.
Recall the major side effects and interactions of Isoniazid, a cornerstone drug for tuberculosis treatment.
The most frequently tested adverse effect of INH is peripheral neuropathy.
Connect this specific side effect to its underlying cause. INH-induced peripheral neuropathy is caused by a deficiency of a specific vitamin.
Evaluate the options provided. The vitamin directly antagonized by INH, leading to neuropathy, is Vitamin B6 (pyridoxine).
Therefore, select Vitamin B6 as the correct answer.

Concept Tested & Keywords

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