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How good are GPs at adhering to a pragmatic trial protocol in primary care? Results from the ADDITION-Cambridge cluster-randomised pragmatic trial
  1. Michael Laxy1,2,3,
  2. Edward C F Wilson4,
  3. Clare E Boothby3,
  4. Simon J Griffin3
  1. 1 Institute of Health Economics, Helmholtz Zentrum München, Neuherberg, Germany
  2. 2 German Center for Diabetes Research, Neuherberg, Germany
  3. 3 MRC Epidemiology Unit, University of Cambridge, Cambridge, UK
  4. 4 Cambridge Centre for Health Services Research, University of Cambridge, Cambridge, UK
  1. Correspondence to Dr Edward C F Wilson; ed.wilson{at}


Objective To assess the fidelity of general practitioners’ (GPs) adherence to a long-term pragmatic trial protocol.

Design Retrospective analyses of electronic primary care records of participants in the pragmatic cluster-randomised ADDITION (Anglo-Danish-Dutch Study of Intensive Treatment In People with Screen Detected Diabetes in Primary Care)-Cambridge trial, comparing intensive multifactorial treatment (IT) versus routine care (RC). Data were collected from the date of diagnosis until December 2010.

Setting Primary care surgeries in the East of England.

Study sample/participants A subsample (n=189, RC arm: n=99, IT arm: n=90) of patients from the ADDITION-Cambridge cohort (867 patients), consisting of patients 40–69 years old with screen-detected diabetes mellitus.

Interventions In the RC arm treatment was delivered according to concurrent treatment guidelines. Surgeries in the IT arm received funding for additional contacts between GPs/nurses and patients, and GPs were advised to follow more intensive treatment algorithms for the management of glucose, lipids and blood pressure and aspirin therapy than in the RC arm.

Outcome measures The number of annual contacts between patients and GPs/nurses, the proportion of patients receiving prescriptions for cardiometabolic medication in years 1–5 after diabetes diagnosis and the adherence to prescription algorithms.

Results The difference in the number of annual GP contacts (β=0.65) and nurse contacts (β=−0.15) between the study arms was small and insignificant. Patients in the IT arm were more likely to receive glucose-lowering (OR=3.27), ACE-inhibiting (OR=2.03) and lipid-lowering drugs (OR=2.42, all p values <0.01) than patients in the RC arm. The prescription adherence varied between medication classes, but improved in both trial arms over the 5-year follow-up.

Conclusions The adherence of GPs to different aspects of the trial protocol was mixed. Background changes in healthcare policy need to be considered as they have the potential to dilute differences in treatment intensity and hence incremental effects.

Trial registration number ISRCTN86769081.

  • diabetes mellitus
  • pragmatic trial
  • protocol adherence
  • primary care

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  • Contributors ML, ECFW, CEB and SJG designed the concept for the paper. ML performed the statistical analysis, interpreted the data and drafted the manuscript. SJG and CEB were involved in collecting the data. ECFW provided statistical support. All authors critically revised the intellectual content of the manuscript and approved its final version.

  • Funding ADDITION-Cambridge was supported by the Wellcome Trust (grant reference No G061895), the Medical Research Council (grant reference no: G0001164), National Health Service R&D support funding (including the Primary Care Research and Diabetes Research Networks), and the National Institute for Health Research. We received an unrestricted grant from University of Aarhus, Denmark, to support the ADDITION-Cambridge trial. Bio-Rad provided equipment to undertake capillary glucose screening by HbA1c in general practice. SJG is a National Institute for Health Research (NIHR) Senior Investigator. The Primary Care Unit is supported by NIHR Research funds. SJG received support from the Department of Health NIHR Programme Grant funding scheme (RP-PG-0606-1259). ECFW is funded by the NIHR Cambridge Biomedical Research Centre.

  • Disclaimer The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Ethics approval Ethical approval was granted by the Eastern Multi-Regional Ethics Committee- UK (ref 02/5/54).

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

  • Data sharing statement The access policy for sharing is based on the MRC Policy and Guidance on Sharing of Research Data from Population and Patient Studies. All data sharing must meet the terms of existing participants' consent and study ethical approvals. Information on data and data requests can be found on In case of questions please contact datasharing@mrc-epid.

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