Objective: To study self-administration and pharmacokinetics (PK) of subcutaneous (SC) belimumab in patients with systemic lupus erythematosus (SLE). Methods: Patients previously treated with belimumab self-administered belimumab 200 mg SC weekly for 8 weeks using an autoinjector. The primary endpoint was the proportion of patients able to self-administer their first and second dose (weeks 1 and 2) in the clinic. The proportion able to self-administer at weeks 4 and 8 (clinic) and weeks 3, 5, 6, and 7 (home) were secondary endpoints. Belimumab PK, safety, and injection-site pain were assessed. Results: 91/95 patients completed the study (withdrawals: adverse events (AEs): 3; lost to follow-up: 1). 93% were female, and mean (SD) age was 44.8 (12.50) years. The majority (99%, 89/90; no attempt, n = 5) successfully self-administered belimumab SC at weeks 1 and 2 (5 had clinic staff assistance), and 98% (85/87) successfully self-administered at weeks 4 and 8. Home-administration success rates were high (93%, (81/87) at weeks 3, 5, 6, and 7). Week 8 median trough concentration was 113 µg/mL. For patients with a ≤ 1.5-week interval between IV SC administration, week-1 concentrations were higher vs. week 8 (+ 51% median) but within a range observed with IV dosing; those with a ≥ 2.5-week interval had median differences close to 0. AEs and serious AEs were low, with no deaths; pain levels were low and decreased with subsequent injections. Conclusion: Patients with SLE successfully self-administered belimumab SC using a novel autoinjector; the PK profile was stable following a switch from IV with acceptable AE and pain levels. The recommended dosing interval between IV to SC dosing is 1 – 4 weeks
