Acquired cyclic neutropenia: successful treatment with prednisone.

A previously healthy woman developed severe, periodic neutropenia after ingestion of phenylbutazone. Oscillations in the monocyte count and hemoglobin concentrations also occurred. The neutropenic episodes were associated with severe bacterial infections requiring hospitalization. Lithium induced a transient interruption in the neutropenia, but continued use was ineffective. Prednisone in a dosage of 100 mg daily successfully interrupted the neutrophil cycling and prevented infection. The patient has remained in remission on 10 mg of prednisone on alternate days.