In patients with moderate-severe systemic lupus erythematosus (SLE), addition of belimumab to standard SLE treatment is safe and improves SLE Responder Index (SRI4) response and decreases disease flare severity compared to placebo plus standard SLE treatment.

• Randomized, double-blind, placebo-controlled study evaluated the safety and efficacy of belimumab in patients with moderate-severe SLE for 52 weeks
• 839 patients were randomized (2:1) to receive belimumab 200mg administered subcutaneously weekly or placebo, in addition to standard SLE treatment
• Primary endpoint: SRI4 at week 52
• Secondary endpoints: corticosteroid dose reduction, time to severe flare
• Adverse events (AEs) and laboratory test results were utilized to assess safety

• 836 patients received treatment (total of 556 belimumab patients, 280 placebo patients)
• 159 patients withdrew before completion of the study
• 61.4% of patients in the belimumab group were SRI4 responders vs 48.4% of patients in the placebo group (OR: 1.68; 95% CI: 1.25, 2.25; P=0.0006)
• Median time to flare was 171 days in the belimumab group vs 118 days in the placebo group (HR 0.51; 95% CI: 0.35, 0.74; P=0.0004)
• A greater number of belimumab patients had a corticosteroid dose reduction of 25% (to 7.5mg/day) vs placebo (18.2% for belimumab group vs 11.9% for placebo group; OR 1.65; 95% CI: 0.95, 2.84; P=0.0732)
• Incidence of AEs was similar between groups
• Serious AEs: reported in 10.8% of belimumab patients vs 15.7% of placebo patients
• 0.9% of belimumab patients had a worsening of IgG hypoglobulinemia by 2 grades vs 1.4% of placebo patients