General Principles

• Aplastic anemia (AA) is a disorder of hematopoietic stem cells that usually presents with pancytopenia.
• Most cases are acquired and idiopathic, but AA can also arise from an inherited BM failure syndrome such as Fanconi anemia, dyskeratosis congenita, and Shwachman–Diamond syndrome.
• Approximately 20% of cases may be associated with drug or chemical exposure (Table 21-5).
  Table 21-5: Commonly Used Drugs That Can Induce Red Blood Cell Disorders

  Sideroblastic Anemia	Aplastic Anemiaa	G6PD Deficiency	Immune Hemolytic Anemia
  Chloramphenicol Cycloserine Ethanol Isoniazid Pyrazinamide	Acetazolamide Antineoplastic drugs Carbamazepine Chloramphenicol Gold salts Hydantoins Penicillamine Sulfonamides Phenylbutazone Quinacrine	Dapsone Doxorubicin Methylene blue Nalidixic acid Nitrofurantoin Pegloticase Phenazopyridine Primaquine Rasburicase Sulfacetamide Sulfamethoxazole Sulfanilamide Sulfapyridine	Cephalosporins (cefotetan, ceftriaxone) Penicillins (piperacillin) Purine nucleoside analogues (fludarabine, cladribine) NSAIDs (diclofenac, ibuprofen) Quinidine Quinine Rifampin Sulfonamides (trimethoprim/sulfamethoxazole)

  Data compiled from multiple sources. Agents listed are available in the United States.

  a Drugs with ≥30 cases reported; many other drugs rarely are associated with aplastic anemia and are considered low risk.

  G6PD, glucose-6-phosphate dehydrogenase.

• Approximately 10% of cases are associated with viral illnesses (e.g., viral hepatitis, Epstein–Barr virus, cytomegalovirus [CMV]).
• Clonal hematopoiesis is a feature of AA, with MDS and acute myeloid leukemia (AML) developing in ∼15% of patients.