These results partly support existing literature indicating an increased risk of adverse events with the use of bDMARDs compared to tDMARDs,[6, 15-17] and they provide evidence of elevated risk for patients who use adalimumab versus Staurosporine etanercept among bDMARDs. Other studies have similarly reported higher bDMARD risks for TB infection,[18-21] but they have also reported higher risk for SBI, which was not confirmed here. These findings

also support an association between bDMARD use and lymphoma risk previously supported largely by adverse event reports. Although the relative risk for TB and lymphoma events was higher than for SBI, these events were uncommon. Only 406 TB events occurred in 61 930 patient years of exposure, and 33 lymphoma events occurred in 63 200 patient years of exposure. The increased lymphoma risk in bDMARD compared to tDMARD cohorts observed in this study could also be the result of residual unbalanced disease activity between the two cohorts, despite propensity score matching. Several studies have found a strong relationship between RA inflammatory activity and lymphoma[33-36] which would account for the increase in risk for lymphoma found in this study. Specifically, the observed higher risk of lymphoma could be the result of common genetic risk factors for RA malignancy, Angiogenesis inhibitor predisposition and severity.[33, 37] As an example, the human leukocyte antigen (HLA)-DRB1 shared-epitope

genotype is affiliated with death related to malignancy in RA.[38] Additionally, there is a level of skepticism concerning the potential impact of bDMARD or other treatments on site-specific risk of cancer in RA[33, 36] which further bolsters the theory of the influence of

residual disease activity on increased lymphoma risk in these patients. As noted, previous studies have shown increased bacterial infection risk associated with bDMARD use.[15] However, other studies have applied a broader definition of SBI, most commonly as any infection that led to hospitalization or death, or required intravenous (i.v.) antibiotics.[6, 15, 16, 24] Other research has HAS1 recorded any infection that fell under general adverse event guidelines,[17] while other studies have evaluated only TB events.[18, 25] Additionally, this study followed a population for a total of 10 years, capturing data on all patients who initiated DMARD use in that time period from the time of treatment initiation. To increase the precision of this study, results were based on person years and adjusted to account for the time patients were persistent on DMARDs. Additionally, propensity score matching was used to help determine the extent of events attributable to medication. Patients receiving bDMARDs showed several differences in baseline characteristics than did patients on tDMARDs, which might have confounded infection risk estimates without the use of propensity matching as performed in this study.