Psoriatic arthritis: the role of self-reported non-adherence, non-trough drug levels, immunogenicity and conventional synthetic DMARD co-therapy in adalimumab and etanercept response

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Objective: The aim of this study was to assess the relationship between self-reported non-adherence, non-trough drug levels, immunogenicity and conventional synthetic DMARD (csDMARD) co-therapy in TNF inhibitor (TNF-i) drug response in PsA. Methods: Serum samples and adherence questionnaires were collected at baseline, 3, 6 and 12 months for PsA patients prescribed TNF-i. Non-trough adalimumab (ADL) and etanercept (ETN) drug levels were measured at 3 and 6 months using commercially available ELISAs. Clinical response was assessed using PsA response criteria (PsARC) and change in 28-joint DAS (DDAS28) between baseline and 3, 6 and 12 months. Results: In 244 PsA patients (52.5% ADL and 47.5% ETN), self-reported non-adherence was associated with PsARC non-response over 12 months using generalized estimating equation (GEE) modelling (P = 0.037). However, there was no significant difference between non-trough ADL or ETN drug levels based on self-reported non-adherence. Higher ETN levels at 3 months were associated with PsARC response at 3 (P = 0.015), 6 (P = 0.037) and 12 months (P = 0.015) and over 12 months using GEE modelling (P = 0.026). Increased ADL drug levels at 3 months were associated with greater DDAS28 at 3 months (P = 0.019). ADL anti-drug antibody-positive status was significantly associated with lower 3- and 6-month ADL levels (P < 0.001) and DDAS28 and PsARC response at 3, 6 and 12 months. Meanwhile, MTX co-therapy was associated with a reduction in immunogenicity at 3 and 6 months (P = 0.008 and P = 0.024). Conclusion: Although both were associated with reduced response, the objectively measured non-trough drug levels showed more significant associations with drug response than self-reported non-adherence measures.

Original languageEnglish
Article numberrkae014
Pages (from-to)rkae014
JournalRheumatology Advances in Practice
Issue number1
Early online date30 Jan 2024
Publication statusPublished - 30 Jan 2024
Externally publishedYes

Data Availability Statement

The data that support the findings of this study are available from the corresponding author (J.B.) on reasonable request. The data are not publicly available owing to privacy/ethical restrictions.


An acknowledgement of thanks is given to Ilinca Lazar (University of Manchester Research Technician) for her assistance in the collection of drug levels and anti-drug antibody levels.


  • TNF inhibitors
  • drug levels
  • drug response
  • immunogenicity
  • non-adherence
  • psoriatic arthritis

ASJC Scopus subject areas

  • Rheumatology

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