Isoniazid (INH) causes deficiency of which vitamin?

Appeared in: NORCET 9 Mains - 2025

Explanation

Isoniazid (INH), a primary drug for tuberculosis, directly interferes with the metabolism of Vitamin B6 (pyridoxine).
INH binds to and inactivates pyridoxal 5'-phosphate, the active form of vitamin B6, leading to its increased excretion and a functional deficiency.
This deficiency is the primary cause of INH-induced peripheral neuropathy, characterized by tingling, numbness, or burning in the hands and feet.
Due to this known side effect, pyridoxine supplementation is a standard part of care for patients on INH therapy, especially those at higher risk (e.g., diabetes, alcoholism, malnutrition).

Option A: Vitamin B1 (thiamine) deficiency is not a characteristic side effect of Isoniazid. Its deficiency is primarily linked to chronic alcoholism.
Option C: Isoniazid does not cause Vitamin B12 deficiency. B12 deficiency is typically caused by malabsorption issues like pernicious anemia or long-term use of drugs like metformin.
Option D: Vitamin K deficiency is related to blood clotting and is not caused by Isoniazid. It can be induced by warfarin, liver disease, or broad-spectrum antibiotics that disrupt gut flora.

Visual 1: Infographic: A visual guide showing how Isoniazid (INH) antagonizes Vitamin B6, leading to peripheral neuropathy.
Visual 2: Chart: A comparison table of B-complex vitamins (B1, B6, B12), their functions, and deficiency symptoms.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Isoniazid-induced vitamin deficiency as background academic context rather than a clinical decision trigger.
Nurses must assess patients on INH for early signs of peripheral neuropathy (tingling, numbness, burning sensations) at every visit.
It is a critical nursing responsibility to ensure that at-risk patients (e.g., those with diabetes, HIV, malnutrition, or alcoholism) receive the prescribed prophylactic pyridoxine.
Patient education should include the importance of taking pyridoxine with INH and reporting any new neurological symptoms immediately to the healthcare provider.

How to Approach the Question

Identify the core of the question: It asks for a specific side effect of the drug Isoniazid (INH).
Recognize this as a factual recall question based on pharmacology knowledge.
Recall the major adverse effects of common antitubercular drugs.
Specifically for INH, remember that the two most classic, testable side effects are hepatotoxicity and peripheral neuropathy.
Connect the peripheral neuropathy to its underlying biochemical cause: Vitamin B6 deficiency.
Scan the options and select Vitamin B6.

Concept Tested & Keywords

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Practise the full NORCET 9 Mains - 2025

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