Leukopenia in Multiple Sclerosis Patients on Peginterferon-B-1a

Background: Despite the approval of oral and newer intravenous agents for treatment of multiple sclerosis, many patients still choose to start or continue interferon beta therapy based on the perceived safety of this class of medication. Peginterferon β-1a provides a less frequent injection schedule (every 2 weeks) with a reduction in annualized relapse rate similar to intramuscular interferon-β-1a.  The most common adverse effects in the phase III peginterferon β-1a phase 3 trial—injection site erythema, influenza-like illness, pyrexia, and headache –were similar to those reported for other interferon preparations. Potentially clinically significant hematology lab abnormalities were reported in only 1% of patients treated with peginterferon β-1a every 2 weeks.

Objectives: To review cases of peginterferon-β-1a induced leukopenia and discuss treatment implications in a real-world setting 

Methods: Case series and literature review

Results: Three Caucasian females (ages 46-51) with multiple sclerosis began treatment with peginterferon-β-1a in 2015.  One patient was taking interferon-β-1a IM prior to initiation of peginterferon-β-1a ; the other two were treatment-naïve. All 3 patients had a normal baseline WBC (k/цL) 5.78-6.45. Leukopenia persisted after 1 year of treatment in all 3 cases with a nadir WBC between 2.72-2.84 k/цL. Two patients had resolution of leukopenia after discontinuing therapy. One patient continues peginterferon-β-1a with close monitoring.  No serious infections were seen among these patients despite the sustained leukopenia.  One patient reported more significant flu-like side effects with peginterferon-β-1a compared to interferon-β-1a IM.

Conclusions: The presence of leukopenia following initiation of peginterferon-β-1a in this series of patients highlights the need for additional real-world safety data for this medication, particularly for those patients considering a switch among interferon preparations.  A systematic review is underway to evaluate the incidence of leukopenia among all patients from a large MS center taking this medication.