Use of pegylated interferon in hypereosinophilic syndrome.

Scant information exists about pegylated interferons (PEG-IFNs) use for treating hypereosinophilic syndrome (HES). We describe 6 patients with HES-1 patient with a newly identified chromosomal abnormality-who received PEG-IFNs. PEG-IFN alpha-2b replaced interferon (IFN) alpha-2b for 4 patients and was initial treatment of 2 patients. PEG-IFN alpha-2a was substituted when PEG-IFN alpha-2b became unavailable. PEG-IFNs were well tolerated and controlled eosinophilia. The dose of PEG-IFNs often could be tapered and the interval between doses lengthened beyond 7 days. Adverse effects included dose-related increases in liver enzyme levels, hair loss, mild lymphopenia, and neutropenia. PEG-IFNs are effective treatment of HES.