agranulocytosis
n. a decline in the number of certain white blood cells (neutrophils), typically as a result of an immune reaction to a drug or other chemical or the toxic effect of this substance on the bone marrow, causing production of white blood cells to fall. Agranulocytosis is diagnosed when the neutrophil count is below 200/mm3 or when the total white-blood-cell count is below 500/mm3. The condition results in suppression of the immune response, rendering individuals vulnerable to opportunistic infections. Psychotropic drugs, such as clozapine and phenothiazine antipsychotics, can induce agranulocytosis.