Use of a baseline risk score to identify the risk of serious infectious events in patients with rheumatoid arthritis during certolizumab pegol treatment

Background: The risk of serious infectious events (SIEs) is increased in patients with rheumatoid arthritis (RA). The aim of this study was to develop an age-adjusted comorbidity index (AACI) to predict, using baseline characteristics, the SIE risk in patients with RA treated with certolizumab pegol (CZP). Methods: Data of CZP-treated patients with RA were pooled from the RAPID1/RAPID2 randomized controlled trials (RCT CZP) and their open-label extensions (All CZP). Predictors of the first SIE were examined using multivariate Cox models. The AACI was developed by assigning specific weights to patient age and comorbidities on the basis of relative SIE risk. SIE rates were predicted using AACI score and baseline glucocorticoid use, and they were compared with observed rates. The percentage of patients in each SIE risk group achieving low disease activity (LDA)/remission was examined at 1 year of treatment. Results: Among 1224 RCT CZP patients, 40 reported ≥ 1 SIE (incidence rate [IR] 5.09/100 patient-years [PY]), and 201 of 1506 All CZP patients reported ≥ 1 SIE (IR 3.66/100 PY). Age ≥ 70 years, diabetes mellitus, and chronic obstructive pulmonary disease/asthma made the greatest contributions to AACI score. SIE rates predicted using AACI and glucocorticoid use at baseline showed good agreement with observed SIE rates across low-risk and high-risk groups. At 1 year, more high-risk All CZP patients than low-risk All CZP patients reported SIEs (IR 8.4/100 PY vs. IR 3.4/100 PY). Rates of LDA/remission were similar between groups. Conclusions: AACI and glucocorticoid use were strong baseline predictors of SIE risk in CZP-treated patients with RA. Predicted SIE risk was not associated with patients' likelihood of clinical response. This SIE risk score may provide a valuable tool for clinicians when considering the risk of infection in individual patients with RA. Trial registration: ClinicalTrials.gov, NCT00152386(registered 7 September 2005); NCT00160602(registered 8 September 2005); NCT00175877(registered 9 September 2005); and NCT00160641(registered 8 September 2005).