Less common causes include Deficiency of vitamin B6 (pyridoxine) or copper (possibly caused by zinc ingestion, which prevents absorption of copper in the gastrointestinal tract) Medications (eg, chloramphenicol, cycloserine, isoniazid, linezolid, pyrazinamide) Toxins (including ethanol and lead) Deficient reticulocyte production, intramedullary death of red blood cells (RBCs), and bone marrow erythroid hyperplasia (and dysplasia) occur.