A 50-year-old Caucasian male with chronic renal failure with two failed cadavaric kidney transplants was evaluated after multiple admissions for life-threatening febrile neutropenia. The absolute neutrophil counts (ANC) had ranged from 165–988/mm3 in the previous year. No cause was identified. A bone marrow aspirate revealed normal trilineage hematopoiesis without dysplasia and cytogenetic analysis demonstrated 46 XY. Core biopsy revealed adequate cellularity. A blood antineutrophil antibody test was positive confirming a diagnosis of autoimmune neutropenia (AIN). Treatment with prednisone was initiated. Although the patient responded to prednisone (100mg/day), evidenced by the ANC increasing to 5544/mm3, he developed massive shifts in weight secondary to fluid retention which complicated dialysis. Additionally he had mild to moderate steroid induced psychosis and sleep disturbances. Attempts at decreasing the dose of prednisone resulted in a decrease in the ANC as well. Therefore, treatment with filgastrim at 300 mcg SQ daily was initiated. The ANC rapidly increased from 571 to 16,578/mm3. Treatment was then switched to pegfilgastrim 6 mg SQ every 3 weeks for ease of administration. An initial ANC increase to 16,000/mm3 was noted; however, by week 3 the ANC had decreased to 448mm3. As a result, the treatment schedule was changed to pegfilgastrim 6 mg SQ every 2 weeks. Since this adjustment, the ANC has consistently ranged from 1500–20,000/mm3. Additionally, there have been no other infections. Pegfilgastrim has already been shown to be as effective as filgastrim in cancer chemotherapy patients, providing a more convenient and tolerable alternative to filgastrim. To date there have been no documented uses of pegfilgastrim in AIN patients. It is logical to assume that pegfilgastrim would have similar efficacy in AIN as well. It was this assumption that first lead to its use in our patient. However, dosing every two weeks rather than the standard every 3 weeks was necessary to achieve the desired effect.

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