• Tumor necrosis factor (TNF) inhibitors — a type of biologic — are effective treatments for rheumatoid arthritis (RA) and psoriatic arthritis (PsA), but they can increase the risk of serious infection.
• People with RA are more likely than people with PsA to have a serious infection following treatment with TNF inhibitors, according to a recent study.
• Risk factors among people with RA, including more frequent use of prednisolone, may contribute to the increased risk of infection, researchers noted.

Following TNF inhibitor treatment, people with RA develop serious infections at nearly twice the rate as those with PsA, according to a recent research study. The findings may help guide health care providers in how they prescribe TNF inhibitors — a type of biologic — for people with different types of rheumatological conditions.

The study was published in Annals of the Rheumatic Diseases and used data collected by the NORwegian-Disease Modifying Anti-Rheumatic Drug (NOR-DMARD) registry, a large collection of information about responses to drug treatments over time.

RA and PsA are both forms of arthritis, an autoimmune disease that affects the joints. Autoimmune diseases arise when the immune system, which normally protects the body from infection, malfunctions and attacks the body’s own tissues. Whereas RA isn’t always linked to another disease, PsA specifically occurs in people with psoriasis.

Response to TNF Inhibitors

Rheumatoid arthritis and psoriatic arthritis may be treated with a class of drugs called tumor necrosis factor inhibitors, which helps to prevent the autoimmune response by making the immune system weaker. While this alleviates symptoms of arthritis, TNF inhibitors can increase the chance of serious infections, such as gastrointestinal (GI) and subcutaneous tissue (the deepest layer of skin) infections.

Examples of TNF inhibitors used to treat psoriatic arthritis include Cimzia (certolizumab pegol), Enbrel (etanercept), and Humira (adalimumab). The research study does not identify specific TNF inhibitors used to treat RA or PsA.

Researchers sought to determine whether one form of arthritis had a higher risk of serious infection after using TNF inhibitors compared to the other. To perform this comparison, the research team used information collected by the NOR-DMARD between 2009 and 2018 that looked at how people with RA and PsA responded to TNF inhibitors.

The treatment data from the NOR-DMARD was then connected to the Norwegian Patient Registry and the Norwegian Cause of Death Registry to identify people who had had a serious infection — a diagnosed infection that resulted in a hospital stay or death.

The study found that, across the same age and gender, people with PsA were less likely than people with RA to have a serious infection at 12 and 24 months after starting treatment with TNF inhibitors. The incidence rate for serious infections was significantly lower in people with PsA (2.16) compared to the rate in people with RA (4.17). Incidence rates are the total number of cases in a given time period divided by the total number of persons in the population.

The study presents an important finding regarding risk of serious infection among people in treatment for PsA, which has not been as well studied as RA. The conclusion is further supported by the use of real clinical data collected from several hospitals.

Researchers suggested reasons why people with RA may be at higher risk of developing infections after TNF inhibitor treatment. “The additive effect of multiple risk factors in the RA population, including more frequent prednisolone use, may explain some of the increased risk of [serious infections] in patients with RA. Another explanation could be the RA disease itself, through disease-related alterations in host defence.”

The authors noted, however, that the study results “need to be interpreted with caution given the many important differences between the RA and PsA population,” including possible effects from other medications people may take.