Patient demographics and baseline disease characteristics (FAS)
| Placebo Q4W (n=60) | BKZ 16 mg Q4W (n=61) | BKZ 64 mg Q4W (n=61) | BKZ 160 mg Q4W (n=60) | BKZ 320 mg Q4W (n=61) | All patients (n=303) | |
| Age, years, mean (SD) | 39.7 (10.3) | 43.3 (12.6) | 40.4 (10.9) | 42.4 (13.1) | 45.0 (11.4) | 42.2 (11.8) |
| Sex (male), n (%) | 49 (81.7) | 53 (86.9) | 52 (85.2) | 52 (86.7) | 50 (82.0) | 256 (84.5) |
| Caucasian, n (%) | 60 (100) | 58 (95.1) | 60 (98.4) | 59 (98.3) | 61 (100) | 298 (98.3) |
| HLA-B27 positive, n (%) | 57 (95.0) | 51 (83.6) | 56 (91.8) | 52 (86.7) | 54 (88.5) | 270 (89.1) |
| Time since onset of first symptoms, years, mean (SD) | 14.1 (8.4) | 16.2 (10.6) | 12.4 (8.3) | 14.8 (10.3) | 15.3 (10.6) | 14.6 (9.7) |
| Time since diagnosis, years, mean (SD) | 6.6 (7.2) | 8.0 (9.4) | 7.3 (7.8) | 8.8 (9.2) | 8.8 (8.8) | 7.9 (8.5) |
| ASDAS, mean (SD) | 3.8 (0.9) | 3.9 (0.7) | 4.2 (0.8) | 3.9 (0.8) | 3.9 (0.7) | 3.9 (0.8) |
| hs-CRP, mg/L, mean (SD) | 17.6 (24.6) | 15.2 (17.7) | 23.5 (21.6) | 20.5 (19.3) | 18.4 (20.6) | 19.0 (20.9) |
| BASDAI, mean (SD) | 6.5 (1.4) | 6.7 (1.4) | 6.7 (1.3) | 6.3 (1.3) | 6.5 (1.6) | 6.5 (1.4) |
| BASFI, mean (SD) | 5.6 (2.0) | 5.9 (1.7) | 6.0 (1.8) | 5.6 (2.2) | 5.9 (2.0) | 5.8 (2.0) |
| BASMI, mean (SD) | 4.4 (1.6) | 4.8 (1.7) | 4.7 (1.7) | 4.6 (1.8) | 4.8 (1.8) | 4.7 (1.7) |
| Spinal pain score, mean (SD) | 7.0 (1.7) | 7.2 (1.9) | 7.4 (1.6) | 6.6 (2.0) | 7.3 (1.5) | 7.1 (1.7) |
| PGADA, mean (SD) | 7.0 (1.7) | 7.1 (1.5) | 7.3 (1.6) | 6.5 (1.8) | 7.1 (1.9) | 7.0 (1.7) |
| Previous TNF inhibitor therapy, n (%) | 7 (11.7) | 8 (13.1) | 7 (11.5) | 7 (11.7) | 5 (8.2) | 34 (11.2) |
| Current NSAID therapy, n (%) | ||||||
| 1 | 51 (85.0) | 53 (86.9) | 50 (82.0) | 54 (90.0) | 56 (91.8) | 264 (87.1) |
| 2 | 2 (3.3) | 3 (4.9) | 1 (1.6) | 1 (1.7) | 1 (1.6) | 8 (2.6) |
| Receiving csDMARDs, n (%) | 13 (21.7) | 9 (14.8) | 18 (29.5) | 18 (30.0) | 21 (34.4) | 79 (26.1) |
ASDAS, Ankylosing Spondylitis Disease Activity Score; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; BASMI, Bath Ankylosing Spondylitis Metrology Index; BKZ, bimekizumab; CRP, C reactive protein; csDMARD, conventional synthetic disease-modifying antirheumatic drug; HLA-B27, human leucocyte antigen-B27; NSAID, non-steroidal anti-inflammatory drug; PGADA, patient global assessment of disease activity; Q4W, every 4 weeks; TNF, tumour necrosis factor.