A 56-year-old man on isoniazid therapy develops tingling in his feet. What vitamin deficiency is likely responsible?

• A. Folic acid
• B. Niacin
• C. Vitamin B2 (riboflavin)
• D. Vitamin B6 (pyridoxine)

Answer: (D)

In this scenario where a 56-year-old man on isoniazid therapy develops tingling in his feet, the likely vitamin deficiency responsible is vitamin B6, also known as pyridoxine. Isoniazid is a medication commonly used to treat tuberculosis, but it has a side effect of interfering with the metabolism of vitamin B6.

Vitamin B6 is essential for the synthesis of neurotransmitters, including serotonin and norepinephrine, and is involved in the maintenance of normal nerve function. A deficiency in vitamin B6 can lead to peripheral neuropathy, which manifests as tingling, numbness, and pain in the extremities, characteristic of the symptoms the patient is experiencing.

This effect occurs because isoniazid forms a complex with pyridoxine, limiting its availability for the enzymatic reactions that require it. As a result, patients on prolonged isoniazid therapy are at risk for developing vitamin B6 deficiency, which leads to the described neurological symptoms. Ensuring patients on isoniazid also receive pyridoxine supplements can help prevent these complications.