A medical student has been exposed to a patient with tuberculosis and developed a positive tuberculin test (PPD) but exhibited a normal chest X-ray. Fie is placed on a 6-month course of prophylactic treatment, but subsequently develops peripheral neuropathies. Which one of the following vitamins would be considered a treatment for the neurotoxicity?

The treatment for a positive PPD test (tuberculosis) is isoniazid, which can interfere with vitamin B6 (pyridoxine) function in cells. Pyridoxine is activated to PLP in cells (the active form of the vitamin), and isoniazid blocks this activation. A deficiency of B6 can lead to peripheral neuropathy because B6 is required for the conversion of tryptophan to niacin. In many cases, vitamin B6 is given along with isoniazid to prevent these side effects from occurring (by providing more substrate than the isoniazid can bind to). Isoniazid does not affect thiamine (B1 ), riboflavin (B2 ), niacin (B3 ), orcobalamin (B12 ) metabolism, although riboflavin is required to activate pyridoxine.