We undertook this US multicenter continuation study (GlaxoSmithKline study BEL112233; ClinicalTrials.gov identifier: NCT00724867) to assess long‐term safety and efficacy of belimumab in patients with systemic lupus erythematosus (SLE) who completed the Study of Belimumab in Subjects with SLE 76‐week trial (ClinicalTrials.gov identifier: NCT00410384).

Patients continued to receive the same belimumab dose plus standard therapy; patients previously receiving placebo received 10 mg/kg belimumab. The primary outcome measure was long‐term safety of belimumab (frequency of adverse events [AEs] and damage assessed using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index [SDI], evaluated every 48 weeks [1 study year]). Other assessments included the SLE Responder Index (SRI), flare rates (using the modified SLE Flare Index [SFI]), prednisone use, and B cell levels.

Of 268 patients, 140 completed the study and 128 withdrew. The mean ± SD score on the Safety of Estrogens in Lupus Erythematosus National Assessment version of the SLE Disease Activity Index (SELENA–SLEDAI) at baseline was 7.8 ± 3.86. The mean ± SD SDI score increased by 0.4 ± 0.68 from its value at baseline (1.2 ± 1.51). The overall incidence of treatment‐related and serious AEs remained stable or declined through study year 7. An SRI response was achieved by 41.9% and 75.6% of patients at the study year 1 and study year 7 midpoints, respectively. At the study year 7 midpoint, relative to baseline, 78.2% had achieved a ≥4‐point reduction in the SELENA–SLEDAI score, 98.4% had no new British Isles Lupus Assessment Group (BILAG) A organ domain score and no more than 1 new BILAG B organ domain score, 93.7% had no worsening in the physician's global assessment of disease activity, 20.6% had experienced ≥1 severe SFI flare, the mean decrease in prednisone dose was 31.4%, and the median change in CD20+ B cell numbers was −83.2%.

These long‐term exposure results confirm the previously observed safety and efficacy profiles of belimumab in patients with SLE.