Prolonged treatment with INH leads to deficiency of
First, I need to recall why INH causes B6 deficiency. I remember that INH is a first-line drug for tuberculosis. It's a known fact that INH can interfere with vitamin B6 metabolism. The mechanism involves the inhibition of the enzyme responsible for converting pyridoxine to its active form, pyridoxal phosphate. So, when you take INH long-term, the body can't utilize B6 properly, leading to a deficiency.
Now, looking at the options, the correct answer is B6. The other options might include other B vitamins like B1 (thiamine), B2 (riboflavin), B12 (cobalamin), or others. Let's see why they're wrong. Thiamine deficiency is associated with alcoholism or certain diuretic use, not INH. Riboflavin deficiency is rare and usually due to dietary issues. B12 deficiency is linked to pernicious anemia or malabsorption. Folic acid deficiency could be from folate antagonists, but INH doesn't directly cause that.
The clinical pearl here is to remember that INH-induced B6 deficiency can lead to peripheral neuropathy. So, patients on INH should be supplemented with pyridoxine. That's a high-yield point for exams. Also, knowing the mechanism helps in remembering the answer—INH's interference with B6 metabolism is a key point.
I need to structure the explanation as per the given sections. The core concept is the pharmacological effect of INH on B6. The correct answer explanation should detail the enzyme inhibition. Each wrong option should be addressed with why they're not the answer. The clinical pearl is about the supplementation and neuropathy risk. Finally, the correct answer is B6.
**Core Concept**
Prolonged isoniazid (INH) therapy disrupts **vitamin B6 (pyridoxine)** metabolism. INH inhibits the conversion of pyridoxine to its active coenzyme form, pyridoxal phosphate, essential for amino acid metabolism and neurotransmitter synthesis. This leads to functional B6 deficiency.
**Why the Correct Answer is Right**
INH irreversibly binds to **pyridoxine**, forming a nonfunctional adduct that cannot be utilized by the body. This depletes B6 stores over time, impairing enzyme systems like **serine hydroxymethyltransferase** and **dopamine β-hydroxylase**, increasing the risk of peripheral neuropathy. Supplementation with pyridoxine prevents this complication.
**Why Each Wrong Option is Incorrect**
**Option A: Vitamin B1 (Thiamine)** – Thiamine deficiency is caused by chronic alcoholism or malnutrition, not INH.
**Option C: Vitamin B12 (Cobalamin)** – Cobalamin deficiency stems from malabsorption (e.g., pernicious anemia) or dietary insufficiency, unrelated to INH.
**Option D: Folic Acid** – Folic acid deficiency is linked to folate antagonist drugs (e.g., methotrexate), not INH.
**Clinical Pearl /