Atypical Post-Injection Reactions with Delayed Onset Following Glatiramer Acetate 40 mg: Need for Titration?

Glatiramer acetate (GA) 20 mg/day (GA20) is associated with immediate post-injection reactions (PIRs). For convenience of use, approved GA 40 mg three times weekly (GA40) delivers a similar weekly dose. The dose and concentration of a single GA40 injection are, however, twice as high as for GA20, and post-injection adverse events may differ. Cases of atypical PIRs to GA40 prompted us to systematically monitor such events.

The aim was to characterize atypical PIRs in multiple sclerosis (MS) patients treated with GA40.

Clinical practice data were prospectively collected in consecutive relapsing-remitting MS patients. Descriptive statistics for categorical and continuous variables, Mann-Whitney and Chi-squared tests for baseline comparisons, and Cox regression models for association of variables to first atypical PIRs were applied.

Forty-six out of 173 patients (26.6%) given GA40 experienced any PIRs. Of those, 38 (22.0%) had atypical, 14 (8.1%) had combined typical and atypical, and 26 (15.0%) had recurrent atypical PIRs, most frequently shivering (13.3%) and nausea/vomiting (8.1%). Compared to typical PIRs, onset of atypical PIRs was significantly delayed (median 30 vs 1 min, p < 0.0001), and their median duration longer (median 120 vs 6 min, p = 0.00013). Previous exposure to GA20 was associated with a lower risk of atypical PIRs [hazard ratio (HR) = 0.35, 95% confidence interval (CI) 0.17-0.72, p = 0.0039]. Patients experiencing PIRs with GA20 were at elevated risk for atypical PIRs with GA40 (HR = 5.75, 95% CI 1.66-19.94, p = 0.0059).

Atypical PIRs with GA40, especially gastrointestinal symptoms and/or fever/shivering, had a delayed onset and occurred in a significant proportion of our patients. Their real prevalence should be assessed in appropriately designed studies accounting for  nocebo responses. Initial dose titration might reduce PIR frequency.