Acquired agranulocytosis is a rare disorder characterized by a severe decrease in white blood cells (granulocytes) and is usually caused by drugs used to treat cancer, such as chemotherapy, and antipsychotic medications, such as clozapine, which interfere with the production of granulocytes in the bone marrow. The decrease in granulocytes makes individuals with acquired agranulocytosis more susceptible to bacteria infections from bacteria that would otherwise not be considered harmful in a healthy individual.

Early symptoms of acquired agranulocytosis are usually a bacterial infection that may include weakness, extreme fatigue, fever, chills, and infected ulcerations in the mucous membranes of the mouth, throat, and intestinal tract, along with difficulty swallowing (dysphagia) and irritation, pain, and swelling due to the ulcers. As the reduction in granulocytes (granulocytopenia) continues, patients with acquired agranulocytosis may develop an enlarged spleen (splenomegaly) and neutropenia (decreased blood neutrophils). In addition to the early symptoms, individuals with chronic acquired agranulocytosis may experience the development of canker sores in the mouth and gingivitis (inflammation of the gums) that regularly recurs.

The standard treatment for acquired agranulocytosis is the drug, filgrastim (Neupogen), in addition to identifying and discontinuing other drugs that may be causing the disorder. Some patients with acquired agranulocytosis may require treatment with antibiotics or corticosteroid therapy for associated bacterial infections. Immunocompromised patients with acquire agranulocytosis may require gamma globulin infusions. The associated mouth and throat ulcers can be treated with saline or hydrogen peroxide gargles, anesthetic lozenges, and antifungal mouthwashes containing the drug, nystatin, for oral fungal infections, such as thrush or Candida albicans (yeast infection). A liquid diet may be necessary until the ulcers heal. Acquired agranulocytosis will usually resolve once the granulocyte levels return to normal.