Conference Coverage

Placebo response in negative rituximab BeatMG trial provides important lessons


 

REPORTING FROM AANEM 2019

– Among patients with acetylcholine receptor (AChR) antibody-positive generalized myasthenia gravis, rituximab and placebo may have a similar glucocorticoid-sparing effect regardless of disease severity, according to research presented at the annual meeting of the American Association of Neuromuscular and Electrodiagnostic Medicine.

Richard Nowak, MD, assistant professor of neurology and director of the Yale Myasthenia Gravis Clinic in New Haven, Conn. Jake Remaly/MDedge News

Dr. Richard Nowak

B Cell Targeted Treatment In Myasthenia Gravis (BeatMG) was a 52-week, randomized, double-blind, placebo-controlled clinical trial. The phase 2 study’s primary outcomes were safety and the glucocorticoid-sparing effect assessed by the percentage of patients who reduced their mean daily prednisone dose by at least 75% and maintained clinical stability. Secondary outcomes were change in Myasthenia Gravis Composite (MGC) score and change in Quantitative Myasthenia Gravis (QMG) score from baseline to 52 weeks.

Investigators randomized 52 participants 1:1 to rituximab (Rituxan) or placebo. Patients were taking at least 15 mg/day of prednisone and were a mean of about age 50 years. About two-thirds were treated with glucocorticoids alone at baseline, and nearly two-thirds had a Myasthenia Gravis Foundation of America (MGFA) clinical classification of II. “It was a mildly symptomatic group of individuals in terms of disease severity,” said Richard Nowak, MD, assistant professor of neurology and director of the Yale Myasthenia Gravis Clinic in New Haven, Conn.

During the study, 60% of patients who received rituximab had a 75% or greater reduction in their mean daily prednisone dose and maintained clinical stability. “However, what surprised us is that we had a significantly high placebo response rate of 56%,” he said. The difference between groups was not significant.

Patients who received rituximab had “directionally favorable reductions” in MGC and QMG scores over 52 weeks, compared with patients who received placebo. Nevertheless, “after correcting for baseline differences, there was no significant difference between the two groups,” Dr. Nowak said.

Rituximab had good safety and tolerability, and the placebo group had a threefold higher rate of clinical relapse requiring IV immunoglobulin or plasmapheresis. “While the placebo arm did achieve a similar rate of reduction in their steroid dose, at 52 weeks the patients may have been doing less well, reflected by the higher rate of relapse,” he said.

Subgroup analysis

To explore whether rituximab might benefit patients who were treatment resistant or had more symptomatic disease, Dr. Nowak and his colleagues conducted a post hoc subgroup analysis of 20 participants – 10 in the rituximab arm and 10 in the placebo arm – who were MGFA class III-IV. In each group, 70% were on glucocorticoid treatment alone, and 90% were MGFA class III.

As in the overall study, the glucocorticoid-sparing effect was not significant (60% of the rituximab group vs. 50% of the placebo group).

Mean change in QMG score was –3.9 in the rituximab group and –0.5 in the placebo group, and mean change in MGC score was –7.0 in the rituximab group and –4.8 in the placebo group. These secondary outcomes again show “directional favorability” with rituximab, Dr. Nowak said. The researchers saw similar trends for scores that assess quality of life and activities of daily living.

In the subgroup analysis, myasthenia gravis relapses requiring rescue therapy occurred in 20% of patients in the rituximab arm and in 30% of the placebo arm. Overall, the researchers did not see a difference in treatment response between those with moderate to severe disease and those with mild disease, Dr. Nowak said.

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