Bone marrow suppression

Bone marrow suppression also known as myelotoxicity or myelosuppression, is the decrease in production of cells responsible for providing immunity (leukocytes), carrying oxygen (erythrocytes), and/or those responsible for normal blood clotting (thrombocytes). Bone marrow suppression is a serious side effect of chemotherapy and certain drugs affecting the immune system such as azathioprine. The risk is especially high in cytotoxic chemotherapy for leukemia. In the case of non-small-cell lung cancer, myelosuppression predisposition was shown to be modulated by enhancer mutations.

Nonsteroidal anti-inflammatory drugs (NSAIDs), in some rare instances, may also cause bone marrow suppression. The decrease in blood cell counts does not occur right at the start of chemotherapy because the drugs do not destroy the cells already in the bloodstream (these are not dividing rapidly). Instead, the drugs affect new blood cells that are being made by the bone marrow. When myelosuppression is severe, it is called myeloablation.

Many other drugs including common antibiotics may cause bone marrow suppression. Unlike chemotherapy the effects may not be due to direct destruction of stem cells but the results may be equally serious. The treatment may mirror that of chemotherapy-induced myelosuppression or may be to change to an alternate drug or to temporarily suspend treatment.

Because the bone marrow is the manufacturing center of blood cells, the suppression of bone marrow activity causes a deficiency of blood cells. This condition can rapidly lead to life-threatening infection, as the body cannot produce leukocytes in response to invading bacteria and viruses, as well as leading to anaemia due to a lack of red blood cells and spontaneous severe bleeding due to deficiency of platelets.

Parvovirus B19 inhibits erythropoiesis by lytically infecting RBC precursors in the bone marrow and is associated with a number of different diseases ranging from benign to severe. In immunocompromised patients, B19 infection may persist for months, leading to chronic anemia with B19 viremia due to chronic marrow suppression.

Bone marrow suppression due to azathioprine can be treated by changing to another medication such as mycophenolate mofetil (for organ transplants) or other disease-modifying drugs in rheumatoid arthritis or Crohn's disease.

Bone marrow suppression due to anti-cancer chemotherapy is much harder to treat and often involves hospital admission, strict infection control, and aggressive use of intravenous antibiotics at the first sign of infection.

G-CSF is used clinically (see Neutropenia) but tests in mice suggest it may lead to bone loss.