PHILADELPHIA — Septic arthritis was twice as common in patients taking anti–tumor necrosis factor drugs for rheumatoid arthritis as in patients with the disease who did not take anti-TNFs.
However, the results may not be fully translatable to a U.S. population of RA patients, according to Dr. Deborah P. Symmons, who presented the findings during a press briefing at the annual meeting of the American College of Rheumatology.
In the United Kingdom, she explained, patients must have failed two disease-modifying antirheumatic drugs and have a high disease activity score in order to be eligible for treatment with TNF blockers. “Those people may have more serious disease” than do those in the United States, said Dr. Symmons, professor of rheumatology and musculoskeletal epidemiology at the University of Manchester (England).
Dr. Symmons and her associates studied the records of 11,757 RA patients from the British Society for Rheumatology Biologics Register who received anti-TNF drugs from October 2001 through May 2008. Patients were followed for 6 months or until death. Septic arthritis was counted in all patients who received that diagnosis either while taking anti-TNFs or within 90 days of their last dose. The control group was 3,515 patients with active RA who were taking only DMARDs.
According to Dr. Symmons, 179 cases of septic arthritis that met study criteria occurred during the study period, for an incident rate of 1 per 200 patients (5 cases per 1,000 patient-years). In contrast, among the DMARD-only control group, there were 17 cases of septic arthritis, for an incidence of 1.9 cases per 1,000 patient-years.
That amounted to a hazard ratio for contracting septic arthritis of 2.0 for the anti-TNF patients, compared with controls (95% confidence interval, 1.1–3.5) after adjustment for age, sex, disease severity, prior joint replacement, comorbidity, and steroid use.
Additionally, the investigators reported that 51% of septic arthritis cases occurred in patients' “native” joints (that is, not prosthetic joints), which are generally considered to have a higher risk of septic arthritis. However, “in both groups, having a replaced joint increased the patient's risk for an infection, but that risk was not further increased by use of an anti-TNF drug,” said Dr. Symmons.
The risk was highest with the use of etanercept, compared with infliximab and adalimumab. Staphylococcus bacteria made up 50% of infection in the DMARD group, and fully 75% of infections in the anti-TNF group.
Dr. Symmons reported affiliation with the British Society for Rheumatology. The researchers wrote that they had no other conflicts to disclose.
Use of an anti-TNF agent did not increase the risk of septic arthritis more than did having a prosthetic knee.
Source DR. SYMMONS