Inhibition of which of the following vitamin is caused by Isoniazid?

Isoniazid inhibits pyridoxal phosphokinase You know that the biologically active form of pyridoxine is pyridoxal phosphate.Thus, Isoniazid inhibits the formation of the active form of B6. Vitamin B6 (pyridoxine) supplementation during isoniazid (INH) therapy is necessary in some patients to prevent the development of peripheral neuropathy. As Vit B6 (PLP) is required for Niacin synthesis from tryptophan, hence Isoniazid therapy also causes Niacin deficiency.