Which type of anemia is associated with isoniazid therapy?

• A. Iron-deficiency anemia
• B. Megaloblastic anemia
• C. Aplastic anemia
• D. Sideroblastic anemia

Answer: (D)

Isoniazid can cause sideroblastic anemia by depleting vitamin B6 (pyridoxine). Pyridoxine is a necessary cofactor for ALA synthase, the first step in heme synthesis. When B6 is deficient, heme production falters and iron cannot be properly incorporated, so iron accumulates in the mitochondria of erythroid precursors, forming ring sideroblasts. This yields a microcytic, hypochromic anemia with increased iron and ferritin. The fix is to add pyridoxine alongside the antibiotic. Distinguishing from iron-deficiency anemia, which has low iron stores, or megaloblastic anemia, which is macrocytic, or aplastic anemia, which features pancytopenia, helps confirm the sideroblastic pattern linked to B6 deficiency from isoniazid.