Patients transitioning from non

Flu-like symptoms are common adverse events associated with interferon beta relapsing multiple sclerosis therapies. To evaluate the incidence and severity of flu-like symptoms after transitioning from non-pegylated interferons to peginterferon beta-1a and assess flu-like symptom mitigation using naproxen. ALLOW was a phase 3b open-label study in relapsing multiple sclerosis patients. Patients had received non-pegylated interferon for 4 or more months immediately before beginning a 4-week screening period. At baseline, patients switched to peginterferon beta-1a and were randomly assigned (1:1) to continue their current flu-like symptoms management regimen or start twice-daily naproxen 500？mg for 8 weeks. Patients then switched to their preferred regimen and were followed for 48 weeks in total. Of 201 patients, 89.6% did not experience new/worsening flu-like symptoms during their first 8 weeks on peginterferon beta-1a. Flu-like symptom severity remained low in current-regimen and naproxen patients, with no significant between-group differences. Median flu-like symptom duration per injection was 3.2 hours longer with peginterferon beta-1a versus prior interferon, but the 4-week cumulative duration was reduced 49–78%. No new safety signals were identified. Most patients who switched from non-pegylated interferon to peginterferon beta-1a did not experience new/worsening flu-like symptoms. Flu-like symptom duration per injection increased, but the cumulative duration significantly decreased. These data may inform flu-like symptom management guidance