AUSTIN – Most patients with refractory generalized myasthenia gravis achieve clinical response by the 12th week of treatment with eculizumab (Soliris), but up to 16% of patients appear to have a late response to treatment, according to a secondary analysis presented at the annual meeting of the American Association of Neuromuscular and Electrodiagnostic Medicine.

Evidence for the sustained effectiveness of eculizumab, a terminal complement inhibitor, in adult patients with antiacetylcholine receptor antibody-positive refractory generalized myasthenia gravis was provided by the 6-month, double-blind, placebo-controlled REGAIN study and its open-label extension. James F. Howard Jr., MD, distinguished professor of neuromuscular disease at the University of North Carolina in Chapel Hill and colleagues sought to analyze response profiles in REGAIN and its open-label extension.

The findings raise the possibility that complement inhibition with eculizumab should not be abandoned rapidly. “We accept that [eculizumab] works quickly,” Dr. Howard said. “There is an impression that if you don’t respond within the first 3 months, you’re not going to respond. I think these data would suggest otherwise.”

The investigators analyzed participants’ Myasthenia Gravis–Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores, which had been recorded throughout REGAIN and the extension. They defined early and late responses as improvement in MG-ADL score (i.e., a decrease of three or more points) or QMG score (i.e., a decrease of five or more points) occurring at 12 weeks or earlier or after 12 weeks, respectively, after initiation of eculizumab therapy. Patients randomized to eculizumab in REGAIN initially were treated with an IV induction dose of 900 mg/week before receiving 1,200 mg every 2 weeks thereafter.

Dr. Howard and colleagues included 98 patients in their analysis. Approximately 32% of patients achieved their first response within the first week of treatment, and 15% responded at week 2. About 16% of patients had a late response.

Responses to treatment on the MG-ADL scale had occurred in 67.3% by week 12 and in 84.7% by the end of the extension. Treatment with eculizumab resulted in QMG responses in 56.1% by week 12 and 71.4% by the end of the extension. The investigators observed response over multiple consecutive assessments for the vast majority of patients.

At week 130, the least-squares mean percentage changes from baseline in MG-ADL score were −61.9% and −47.5% in early and late MG-ADL responders, respectively. The least-squares mean percentage changes from baseline in QMG score were −40.8% and −55.5% in early and late QMG responders, respectively.

The investigators observed significant baseline differences between early versus late QMG responders in mean duration of myasthenia gravis (10.46 years vs. 5.46 years) and mean QMG score (18.6 vs. 15.1).

“I can’t explain [this finding]. It may simply be due to the low numbers of patients,” Dr. Howard said. “Whether this is going to hold up in postmarketing analysis remains to be seen. I’m not convinced that that is meaningful.”

Study funding was provided by Alexion Pharmaceuticals (the developer of eculizumab), the Centers for Disease Control and Prevention, and the National Institutes of Health. Dr. Howard reported receiving research support and consulting fees or honoraria from Alexion and several other pharmaceutical companies. Several other authors reported financial relationships with Alexion and other pharmaceutical companies; two authors are employees of Alexion.

egreb@mdedge.com

Howard J et al. AANEM 2019. Unnumbered Abstract.

Late response to eculizumab may occur in minority of myasthenia gravis patients