Repository logo

How good are GPs at adhering to a pragmatic trial protocol in primary care? Results from the ADDITION-Cambridge cluster-randomized pragmatic trial

Published version



Change log


Laxy, M 
Wilson, ECF 


Objective: To assess the fidelity of general practitioners’ (GP) 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 multi-factorial treatment (IT) vs. 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 40-69 year old patients 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 cardio-metabolic medication in years 1 to 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 health care policy need to be considered as they have the potential to dilute differences in treatment intensity and hence incremental effect. Clinical trial number: ISRCTN86769081



diabetes mellitus, pragmatic trial, primary care, protocol adherence, Aged, Cardiotonic Agents, Cardiovascular Diseases, Diabetes Mellitus, Type 2, England, Female, General Practice, Guideline Adherence, Humans, Linear Models, Male, Middle Aged, Practice Patterns, Physicians', Pragmatic Clinical Trials as Topic, Retrospective Studies

Journal Title

BMJ Open

Conference Name

Journal ISSN


Volume Title



BMJ Journals
Medical Research Council (MC_UU_12015/4)
Department of Health (via National Institute for Health Research (NIHR)) (NF-SI-0515-10119)
NIHR Central Commissioning Facility (NIHRDH-RP-PG-0606-1259)
Medical Research Council (G0001164)
Wellcome Trust (061895/Z/00/Z)