acute infection characterized by severe sore throat, fever, and fatigue and associated with an extreme reduction of white blood cells, or leukocytes (leukocyte) (a condition known as leukopenia), particularly the white cells known as neutrophils (neutropenia).

In most cases, agranulocytosis appears to develop as a result of sensitization to certain drugs and chemicals; infection then follows as a consequence, not a cause, of the profound neutropenia. First observed as a reaction to the coal-tar product aminopyrine, agranulocytosis is triggered by a variety of pain relievers (analgesics), tranquilizers, antihistamines, anticonvulsants, sulfonamide derivatives, and antithyroid drugs. It also is a frequent complication of cancer treatment. Treatment of agranulocytosis consists of the immediate and permanent withdrawal of the offending drug and control of the infection with antibiotics.