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Managing the selection of placebo group switched to experimental treatment group in post-randomised controlled trial extension studies
  1. Maya H Buch1,2,
  2. Walter P Maksymowych3,
  3. Maarten Boers4
  1. 1 Centre for Musculoskeletal Research, Division of Musculoskeletal and Dermatological Sciences, Faculty of Biology, Medicine & Health, University of Manchester, Manchester, UK
  2. 2 National Institute for Health Research Manchester Biomedical Research Centre, Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK
  3. 3 Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
  4. 4 Department of Epidemiology & Data Science and Amsterdam Rheumatology and Immunology Center, Amsterdam UMC, Vrije Universiteit, Amsterdam, The Netherlands
  1. Correspondence to Professor Maya H Buch, Centre for Musculoskeletal Research, The University of Manchester, Manchester M13 9PL, UK; maya.buch{at}

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Well-designed clinical trial extension studies (TES) can provide robust and meaningful information on the long-term safety, tolerability and efficacy of emergent drugs. A previous 'European Alliance of Associations for Rheumatology (EULAR) initiative established recommendations on the conduct, design and analysis of TES to mitigate potential bias and distortion of long-term outcomes,1 which subsequent post-randomised controlled trial (RCT) TES have applied. As prior participants to this initiative, we highlight an area that needs further consideration, namely the selection of the control group that takes place to switch to experimental therapy.

The objective of TES is to capture outcomes of patients exposed to the experimental drug. The recommendations emphasise the importance of intention-to-treat (ITT) analysis, the denominator being the original number entering the RCT. In the original trial, the purpose of ITT is to capture outcomes for the complete randomised population, regardless of exposure to the intervention, as we …

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  • Handling editor Josef S Smolen

  • Contributors MHB drafted and WPM and MB revised the manuscript. All authors approved the final submitted manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Disclaimer MHB: The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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