“It would seem unusual for drugs acting on the same pathway with similar efficacy to have such drastically different infection risks,” Dr. Rutherford and his coauthors observed in their report.
However, investigators noticed that in the certolizumab pegol cohort, a large number of patients had not previously been on a biologic. When those biologic-naive patients were excluded from analysis, there was no longer a difference in infection rate favoring certolizumab pegol. “This suggests that unmeasured confounders may be responsible for the difference that was observed in the primary analysis,” the investigators said in their discussion of the results.
The Cochrane review showing an increased risk of serious infections with certolizumab pegol was a large network meta-analysis, which they said relies on indirect comparisons between drugs and could be prone to error if there are differences in study design.
“In contrast, national registers use the same methodology for detecting and reporting of adverse events for each drug,” they added.
Dr. Rutherford reported no disclosures. Study coauthors reported disclosures related to Pfizer, AbbVie, Bristol-Myers Squibb, UCB, and Celgene. The British Society for Rheumatology, which commissioned the study, receives income from AbbVie, Celltrion, Hospira, Pfizer, UCB, and Roche related to a different contract.
SOURCE: Rutherford AI et al. Ann Rheum Dis. 2018 Mar 28. doi: 10.1136/annrheumdis-2017-212825.