Isoniazid commonly causes peripheral neuropathy due to a deficiency of which vitamin, and what preventive measure is recommended?

• A. Vitamin B12 deficiency; prevent with B12 supplementation.
• B. Vitamin C deficiency; prevent with vitamin C.
• C. Folic acid deficiency; prevent with folic acid.
• D. Pyridoxine deficiency; prevent with pyridoxine supplementation.

Answer: (D)

Isoniazid can cause peripheral neuropathy because it disrupts vitamin B6 (pyridoxine) metabolism. It acts as a vitamin B6 antagonist, forming a complex with pyridoxal phosphate and increasing its inactivation, which leads to a functional pyridoxine deficiency. Pyridoxine is a crucial cofactor for enzymes that produce neurotransmitters such as GABA and for nerve myelin maintenance; when its availability drops, nerves become susceptible to damage, resulting in neuropathy symptoms like numbness and tingling.

To prevent this adverse effect, pyridoxine supplementation is recommended alongside isoniazid therapy. A common preventive approach is giving a small daily dose of vitamin B6 (for example, around 25–50 mg daily), with higher doses considered for individuals at greater risk. Thus, the correct concept is that neuropathy from isoniazid stems from pyridoxine deficiency and is best prevented with pyridoxine supplementation.