| Adverse events | Placebo + MTX (n = 125)* | Certolizumab pegol 200 mg + MTX (n = 248) | Certolizumab pegol 400 mg + MTX (n = 246) |
| Any treatment-emergent AE | 66 (52.8) | 139 (56.0) | 125 (50.8) |
| Intensity | |||
| Mild | 45 (36.0) | 108 (43.5) | 101 (41.1) |
| Moderate | 32 (25.6) | 61 (24.6) | 57 (23.2) |
| Severe | 5 (4.0) | 17 (6.9) | 14 (5.7) |
| Related | 23 (18.4) | 61 (24.6) | 56 (22.8) |
| Any infections | 26 (20.8) | 69 (27.8) | 53 (21.5) |
| SAE | 4 (3.2) | 18 (7.3) | 18 (7.3) |
| Serious infections | 0 | 8 (3.2) | 6 (2.4) |
| AE leading to death | 0 | 1 (0.4) | 1 (0.4) |
| AE leading to withdrawal | 2 (1.6) | 12 (4.8) | 7 (2.8) |
| Most common AE† | |||
| Urinary tract infection | 9 (7.2) | 11 (4.4) | 5 (2.0) |
| Upper respiratory tract infection | 2 (1.6) | 11 (4.4) | 4 (1.6) |
| Headache | 1 (0.8) | 9 (3.6) | 8 (3.3) |
| Bacteriuria | 4 (3.2) | 8 (3.2) | 6 (2.4) |
| Nasopharyngitis | 1 (0.8) | 8 (3.2) | 4 (1.6) |
| Rheumatoid arthritis | 4 (3.2) | 7 (2.8) | 2 (0.8) |
| Hypertension | 2 (1.6) | 6 (2.4) | 9 (3.7) |
| Haematuria | 5 (4.0) | 4 (1.6) | 4 (1.6) |
| Hepatic enzyme increased | 4 (3.2) | 3 (1.2) | 3 (1.2) |
| AST increased | 5 (4.0) | 2 (0.8) | 6 (2.4) |
| ALT increased | 6 (4.8) | 1 (0.4) | 8 (3.3) |
Results are shown as number (%) of patients.
*Two patients in the placebo group received certolizumab pegol 200 mg and were included in the certolizumab pegol 200 mg group for safety evaluations; †treatment-emergent adverse events occurring in ⩾3% in any group of the safety population.
AE, adverse event; ALT, alanine aminotransferase; AST, aspartate aminotransferase; MTX, methotrexate; SAE, serious adverse event.