From trial data to practical knowledge: qualitative study of how general practitioners have accessed and used evidence about statin drugs in their management of hypercholesterolaemia

British Medical Journal, Oct 24, 1998 by Karen Fairhurst, Garo Huby

Introduction

Use of evidence from clinical trials to underpin routine practice is seen as a key part of achieving a cost effective health service that offers consistent high quality care.(1 2) Evidence based medicine requires doctors to appraise clinical trials critically to determine the best way of managing a patient's clinical problem.(3) Evidence based medicine is seen as particularly problematic in general practice, where clinical problems are presented in complex social and psychological contexts.(4) Although support for the principle of evidence based medicine has been identified among general practitioners,(5) recognised barriers exist to its implementation. Studies that have explored how general practitioners access evidence and translate this into practice suggest that strategies based on critical appraisal might fail because they are based on unrealistic models of how "evidence" is accessed and evaluated.(6-8)

We present findings from a study in which general practitioners reflected on how they access and incorporate into their practice evidence on management of lipid disorders. We chose this subject as data from recent randomised controlled trials, in particular from the Scandinavian simvastatin survival study (4S)(9) and the West of Scotland coronary prevention study (WOSCOPS),(10) have a high profile and direct relevance to primary care, and local prescribing data suggest wide variation between practices in levels of prescribing of statin drugs. We compared general practitioners' accounts of their current practice with results from the two studies. The Scandinavian study produced evidence of around a 30% reduction in risk of myocardial infarction and death in patients with known ischaemic heart disease whose total serum cholesterol concentration was lowered to [is less than] 5.2mmol/l with titrated doses of simvastatin. The Scottish study showed a similar 30% reduction in risk of myocardial infarction and death in middle aged men with moderately raised total serum cholesterol concentrations ([is greater than] 6.5 mmol/l) without pre-existing coronary heart disease whose serum cholesterol concentration was reduced by a mean of 20% with pravastatin. The cost implications of this evidence are recognised(11 12) and whereas the use of statin drugs in secondary prevention is encouraged, their use in primary prevention is not deemed cost effective and is discouraged both in national guidelines(13) and through prescribing advisers in the local setting for this study.

From this material a distinction emerged between "trial data" such as findings from the Scandinavian and Scottish studies on the one hand and "practical knowledge" as practitioners' understanding, acceptance, and use of these "trial data" in practice on the other hand. This differentiation is central to the following presentation of our findings.

We had two aims: firstly, to explore patterns in general practitioners awareness of the trial results and their application in practice, and, secondly, to draw out possible implications of our findings for appropriate strategies to integrate clinical evidence into general medical practice.

Subjects and methods

The main part of the study involved qualitative interviews with general practitioners. We also interviewed relevant hospital specialists to obtain a local secondary care perspective and health board staff to provide insight into the local context in respect of the promotion of clinical effectiveness in Lothian.

Sample selection

To generate a sample representing variation in prescribing patterns for statin drugs and sociodemographic characteristics of practice populations all general practices in Lothian were ranked according to the defined daily dose (DDD)(14) of statin lipid lowering drugs prescribed per patient and then divided into high, medium, and low prescribers. High prescribing practices were defined as those in the highest quarter for defined daily dose per patient prescribed ([is greater than] 1.4), medium prescribing practices as those in the second and third quarter (0.5-1.4), and low prescribing practices as those in the lowest quarter ([is less than] 0.5). Practices were also categorised according to the proportion of their patients for whom deprivation payments were received and the proportion of their patients aged 65 and over. High, medium, and low deprivation practices received deprivation payments for, respectively, 11% or more, 5-10%, or less than 5% of their patients. For age practices were categorised, respectively, as having 9% or more, 7-8%, or less than 7% of their patients aged 65 and over.

These divisions generated 27 categories of general practice. One general practitioner was selected from each category of practice to include general practitioners who differed in sex, ethnic group, and seniority and worked in different sized partnerships. Of the original sample of 27 doctors, 11 declined to participate. Eight of these were replaced by doctors of similar characteristics.

Interviews