Adherence to cardiovascular medication across Scotland

Leslie, Kirstin (2020) Adherence to cardiovascular medication across Scotland. PhD thesis, University of Glasgow.

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Abstract

Introduction
Despite the availability of efficacious drugs, cardiovascular disease (CVD) remains a leading cause of global mortality, and prevalence of CVD is higher in Scotland than in other developed countries. Better understanding of chronic disease management is important in closing the gap between outcomes found in general practice prescribing with clinical trial findings. A key component of disease management is drug adherence, consisting of initiation, implementation, and persistence, and Scotland has valuable nation-wide administrative databases which can be used to study aspects of adherence at a population level. With these datasets, it is possible to define different CVD patient groups, to compare adherence across a range of drug classes and risk-factors, and to assess the association between drug-persistence with subsequent mortality rates.

Methods
Using the Scottish Prescribing Information System (PIS), linked to hospital admissions data (SMR) and death certificates (NRS), we have defined four patient subgroups: primary prevention (n=1,659,566), treatment for symptomatic cardiovascular disease (n = 260,516), secondary prevention (n=25,283), and secondary-prevention-with-treatment (n=23,866).

Within these patient groups, the Treatment Anniversary Model (TAM) and Proportion of Days Covered (PDC) were used to identify broad levels of persistence and implementation to ten different CVD drug-classes. Further multivariate analysis was conducted in four selected drug classes: ACE-inhibitors, antiplatelets, betablockers, and lipid-regulatory drugs. Risk factors considered include sex, age, socioeconomic status, and comorbidity.

Cox-proportional hazards models were then used to investigate the association between drug-persistence with subsequent mortality. Some additional analyses were carried out to investigate possible sources of confounding.

Results
In the unadjusted analysis, adherence tends to be associated with traditional cardiovascular risk factors (male sex, older age, higher deprivation, etc.) across the drug-classes and patient groups studied. Implementation and persistence are lowest in the primary prevention group and highest in the secondary prevention group. In the multivariate analysis, higher levels of persistence were associated with male sex (OR range 1.16 – 1.40) and increased social deprivation (OR range 1.07-1.18) across all drug-classes and patient-groups. Diabetes as a comorbidity was associated with higher persistence for the primary and treatment groups only (OR range 1.07-1.38). There was some inconsistency in the associations observed for age and for depression as a comorbidity.

The relationship observed between persistence and mortality showed a protective association across the patient-groups and drug-classes studied. Adjusting for additional confounders, such as CVD polypharmacy, did not provide additional insights to these analyses and definitions of this may need refined for future study.

Conclusion
This is a longitudinal, Scotland-wide, retrospective study of adherence to cardiovascular drugs (namely, implementation and persistence), with near-universal population coverage. This allows identification of population-level risk factors, and identification of patient groups who may require extra support. While much of these findings replicate those observed in literature review, this is the first study of its scale assessing implementation and persistence to cardiovascular medication in Scotland. It also proves as validation for Scottish administrative datasets in having the potential to assess medication adherence.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Adherence, cardiovascular, prescribing, electronic health records,
Subjects: R Medicine > RA Public aspects of medicine > RA0421 Public health. Hygiene. Preventive Medicine
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Health and Wellbeing > Public Health
Funder's Name: Medical Research Council
Supervisor's Name: Pell, Professor J.P. and McCowan, Professor C.
Date of Award: 3 November 2020
Depositing User: KH Leslie
Unique ID: glathesis:2020-81914
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Jan 2021 08:19
Last Modified: 19 Jan 2021 09:16
URI: http://theses.gla.ac.uk/id/eprint/81914
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