The rates of flu-like symptoms over 3 years were also similar (62%-64%) in the two groups, and influenza-like illness was reported in 55% of those dosed every 2 weeks and in 45% of those dosed every 4 weeks. In addition to influenza-like illness, pyrexia was the most common flu-like symptom reported over 3 years (43%-45%).
About 65%-69% of those in the two groups reported injection-site reactions, with erythema the most common (62%-64%), followed by pain (17%-18%) and pruritus (12%-16%).
Lab abnormalities were comparable with both dosing schedules: Over 3 years, white blood cell counts were reduced in 6% of those on the 2-week schedule, compared with 8% among those on the 4-week schedule. Lymphocyte counts were reduced in 12% and 9% of those on the 2-week and 4-week schedules, respectively. In addition, 8% of those on the 2-week dose and 6% of those on the 4-week dose had low hemoglobin (100 g/L or less) over the 3 years.
Rates of anti-IFN and anti-PEG antibodies associated with both schedules were low, Dr. Kremenchutzkysaid. Over 3 years, 7%-9% tested positive for IFN binding antibody at least once, and 4%-6% of the total were “persistent positive.” Another 9% of those on the 4-week schedule and 6% of those on the 2-week schedule were anti-PEG antibody positive at least once, and 3%-5% of the patients in total had persistent levels. Titers were high in less than 1% of the total.
In ATTAIN, efficacy endpoints were secondary, and included ARR, which was reduced by 25.1% over 3 years among those receiving the dose every 2 weeks, compared with every 4 weeks (P = .0199). By 144 weeks, 30.5% of those on the 2-week schedule and 41.1% of those on the 4-week schedule had experienced a relapse, a significant difference (P = .0070), Dr. Kremenchutzky said.
The proportion of those with CDP by 144 weeks was 15.5% among those on the 4-week schedule, vs. 9.2% among those on the 2-week schedule (P = .0098), he added.
The studies were funded by Biogen Idec. Dr. Newsome and Dr. Kremenchutzky both disclosed having been compensated for activities with Biogen Idec and other companies that market MS drugs.