When discussing chemotherapy side effects you may hear the term nadir used, usually in reference to the blood counts, particularly white blood cell count and platelet count. Nadir basically means low point, however further explanation may clarify this term in connection with chemotherapy treatment.
When chemotherapy is given it not only affects the rapidly dividing cancer cells but it also affects some of the normal cells of the body. These effects particularly occur on normal cells that divide rapidly such as, the hair, the lining of the mouth, the cells lining the intestinal tract and the blood cells (white and red blood cells as well as platelets).
In the bone marrow, the spongy inner core of the larger bones of the body this is where blood cells are made. There are very immature cells called stem cells, from which the various types of blood cells develop. These stem cells do not reproduce quickly and are less likely to be affected by chemotherapy. As cells are maturing there are certain phases in which they divide faster. It is during these times that the cells are most sensitive to chemotherapy. The more mature cells can continue to become fully mature cells for several days after chemotherapy is given. When these cells live out their life span, the circulating supply is depleted and the blood counts fall to a low point, the nadir.
The blood counts will return to normal within three to four weeks, after the body's feedback system has told the stem cells in the bone marrow to increase production and begin making new cells. If chemotherapy is given at the time that the stem cells in the bone marrow are increasing their production this could cause permanent bone marrow damage. The timing of chemotherapy cycles takes this process into account. For example some chemotherapy drugs are given on day 1 and day 8 of a 28-day cycle. The second dose of chemotherapy, one week after the first, is tolerated because the stem cells have not yet increased their production (they are still at the nadir). They have not increased their production because the second treatment is given before the count of the circulating blood has reached its nadir.
The nadir time is usually about 10 days after treatment, although this may vary depending on the drugs given. The concern during the nadir time is that the body's first line of defense against infection, white blood cells (WBC) and the platelets, which help to clot the blood, are low leaving a person more susceptible to infection and bleeding. The next dose of chemotherapy is given only after a person's blood counts have left the nadir and recovered to a safe level.
More Chemotherapy Information:
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