Adherence to biologic therapies and associated factors in rheumatoid arthritis, spondyloarthritis and psoriatic arthritis: a systematic literature review.

Objectives: To analyse the evidence on adherence to biologic therapies in rheumatoid arthris (RA), spondyloarthritis (SpA), and psoriatic arthritis (PsA).
Methods: Systematic review of studies retrieved by a sensitive search strategy in MEDLINE database (1961 through March 2012). To be selected, studies had to include patients with RA, SpA, or PsA, treatment with intravenous or subcutaneous biologic therapies, and had to report on measures of adherence. By design, only randomised controlled trials (RCT) or high quality cohort studies with a control group were selected.
Results: A total of 24 studies were included, of which 12 reported results from national or local biologic registers, 9 were retrospective studies, 2 prospective studies, and only one was an RCT. Patients included were mostly women with diagnosis of RA or SpA and, less frequently, PsA. There was a great variability in the definition of adherence, measurement methods, and associated factors analysed. In general, adherence to etanercept was superior to that of other biologics, by the measures utilised. The main predictive factors - age, sex, comorbidity, baseline clinical condition, previous or concomitant use of DMARDs, anti-TNF in monotherapy or in combination with MTX - produced diverse, even divergent results across studies.
Conclusions: There is a wide variability related to the adherence concept and its measurement, reflecting the complexity of the phenomenon. In order to draw more consistent conclusions about the relative value of predictive factors on adherence and persistence of biological therapy, larger controlled studies with better selection of variables and analysis of interactions are needed.