Determinants of blood pressure lowering treatment prescribing for primary prevention: a cohort study in UK primary care

Date of ISAC Approval: 
08/05/2019
Lay Summary: 
Blood pressure lowering drugs are extremely effective in reducing heart attacks and strokes. In the UK, guidelines recommend that blood pressure drugs are prescribed to patients based on a combination of their blood pressure and their overall cardiovascular risk (which takes into account factors like smoking, diabetes and age and predicts how likely somebody is to have a heart attack or stroke in the next ten years). However, some studies show that doctors don't agree with using risk and might just use high blood pressure to decide on treatment. Our previous study showed that using only cardiovascular risk to decide on a patient's treatment would prevent more heart attacks and strokes than the current UK guidelines. This would mean treating people with high risk, even if their blood pressure was normal, and would rely on doctors understanding and using risk to make treatment decisions. At the moment, it is not clear to what extent blood pressure, risk, or both are influencing use of blood pressure lowering drugs. Therefore, this study aims to investigate whether or not drugs are prescribed when a patient first has high blood pressure, and which factors (blood pressure, risk, age, sex, or other patient factors) mean that a patient is more likely to receive drug treatment. We will also investigate whether these factors are related to control of blood pressure. The results of this study will help us to make future recommendations and provide support for GPs to use guidelines in their everyday practice.
Technical Summary: 
Randomised trials have shown that blood pressure lowering treatment reduces the risk of cardiovascular disease. For primary prevention, the National Institute of Health and Care Excellence (NICE) recommends using a combination of blood pressure and risk to determine eligibility for blood pressure lowering treatment. However, there is some evidence that GPs and patients do not understand, agree with, or use measures of absolute risk in their decision making, and continue to use 'hypertension' alone as an indication for treatment, irrespective of their risk. We have previously shown that an entirely risk-based approach to blood pressure lowering would be at least as efficient and would prevent more cardiovascular disease events than the current and newly proposed NICE guidance. However, if an entirely risk-based strategy is to be implemented, then it will rely on GPs using risk in their decision making for treatment. Therefore, this study aims to investigate current patterns of prescribing of blood pressure lowering treatment among patients with incident hypertension, and which patient-level factors are most strongly related to incident prescription of blood pressure lowering treatment. Furthermore, given the increasing importance of blood pressure control among patients with increasing cardiovascular disease risk, we will determine which patient-level factors are most strongly related to subsequent control of blood pressure. We will conduct a cohort study in CPRD, identifying patients with incident hypertension between 2013 and 2017. The outcome will be a new prescription of blood pressure lowering drugs on the date of diagnosis. We will describe drug use by QRISK2 scores, systolic and diastolic blood pressure, and other patient-level characteristics including age, sex, diabetes, polypharmacy, and comorbidity. We will use logistic regression modelling to investigate the determinants of prescribing, and the determinants of control at six months and one year. The results of this study will guide future recommendations and help to provide support for GPs to translate any new guidelines into clinical practice.
Health Outcomes to be Measured: 
Objectives 1-3: Prescription of blood pressure treatment on date of hypertension diagnosis Objective 4: Control of blood pressure
Collaborators: 

Dr Emily Herrett - Chief Investigator - London School of Hygiene & Tropical Medicine (LSHTM)
Adam Timmis - Collaborator - Queen Mary University of London
Elizabeth Williamson - Collaborator - London School of Hygiene & Tropical Medicine (LSHTM)
Dr Emily Herrett - Corresponding Applicant - London School of Hygiene & Tropical Medicine (LSHTM)
Professor Liam Smeeth - Collaborator - London School of Hygiene & Tropical Medicine (LSHTM)
Reecha Sofat - Collaborator - University College London (UCL)
Rod Jackson - Collaborator - University of Auckland
Professor Tjeerd van Staa - Collaborator - University of Manchester

Linkages: 
HES Admitted;Patient Townsend