Adherence to Antitumor Necrosis Factor Use Recommendations in Spondyloarthritis: Measurement and Effect in the DESIR...

To evaluate a classification system to define adherence to axial spondyloarthritis (axSpA) anti-tumor necrosis factor (anti-TNF) use recommendations and examine the effect of adherence on outcomes in the DESIR cohort (Devenir des Spondylarthropathies Indifférenciées Récentes).

Using alternate definitions of adherence, patients were classified as adherent "timely" anti-TNF users, nonadherent "late" anti-TNF users, adherent nonusers ("no anti-TNF need"), non-adherent nonusers ("unmet anti-TNF need"). Multivariate models were fitted to examine the effect of adherence on quality-adjusted life-years (QALY), total costs, and nonbiologic costs 1 year following an index date. Generalized linear regression models assuming a γ-distribution with log link were used for costs outcomes and linear regression models for QALY outcomes.

Using the main definition of adherence, there were no significant differences between late anti-TNF users and timely anti-TNF users in total costs (RR 0.86, 95% CI 0.54-1.36, p = 0.516) or nonbiologic costs (RR 0.72, 95% CI 0.44-1.18, p = 0.187). However, in the sensitivity analysis, late anti-TNF users had significantly increased nonbiologic costs compared with timely users (RR 1.58, 95% CI 1.06-2.36, p = 0.026). In the main analysis, there were no significant differences in QALY between timely anti-TNF users and late anti-TNF users, or between timely users and patients with unmet anti-TNF need. In the sensitivity analysis, patients with unmet anti-TNF need had significantly lower QALY than timely anti-TNF users (-0.04, 95% CI -0.07 to -0.01, p = 0.016).

The effect of adherence to anti-TNF recommendations on outcomes was sensitive to the definition of adherence used, highlighting the need to validate methods to measure adherence.