Determinants of medication use for the secondary prevention of cardiovascular disease
Keywords: antiplatelet therapy
CVD management
statin
cardiovascular disease

Previous studies have shown that use of effective and widely recommended treatments, specifically statin and antiplatelet therapy, for the secondary prevention of atherosclerotic cardiovascular disease (ASCVD) is suboptimal. However, knowledge regarding the underlying reasons for suboptimal medication use at different treatment stages, including the role of particular individual characteristics, and the variations in medication use across different population groups and ASCVD categories, is limited.
I undertook the first systematic literature review of studies that estimated the proportions and determinants of statin and antiplatelet therapy for the secondary prevention of ASCVD among myocardial infarction and ischaemic stroke patients at every stage of the treatment pathway, namely medication prescription on discharge, initiation of treatment after discharge, adherence to and persistence with treatment. The review presented evidence of gradually increasing, yet suboptimal medication use at almost every stage of the pathway for both statin and antiplatelet therapy. Multiple patient and provider- related risk factors of suboptimal medication use were identified. Women were less likely to receive statin and antiplatelet therapy (except for aspirin) on discharge, and less likely to initiate statin. A U-shaped association was observed for risk of statin discontinuation with age, where elderly individuals aged 69 years or older and those younger than 64 years were at greater risk. Prior CVD and presence of specific physical comorbidities were associated with suboptimal statin use at various treatment stages. Most of these studies had a limited follow-up time and examined a maximum of two treatment stages, thereby limiting the ability to generalise results and insights into the full extent of suboptimal use across the entire treatment pathway and over time.
Using linked NHS Scotland administrative hospitalisation and prescription information data on all individuals in Scotland ever hospitalised for an ASCVD event since 2009 with a follow-up time of up to eight years, I estimated the extent of use and patient characteristics associated with suboptimal statin and antiplatelet therapy use. About 82% and 84% of individuals hospitalised for ASCVD event subsequently initiated statin and antiplatelet therapy, respectively, with rates varying significantly by ASCVD type. Although more than 90% of individuals who initiated statin and/or antiplatelet therapy were adherent while on medication, one quarter of individuals eventually discontinued treatment. Of those who discontinued, 50% of individuals ceased statin and/or antiplatelet therapy within 1.5 years, and 80% within 3.5 years, despite clinical guidelines recommending lifelong treatment. Among individuals who discontinued treatment, 38% and 37% of individuals re-initiated some type of statin and antiplatelet therapy at some point in time, and on average within 1.1 years since discontinuation.
Patient phenotypes that were consistently associated with higher risks of non-initiation and discontinuation of treatment included women, individuals aged below 50 years or above 70 years (compared to those aged 60 to 69 years), individuals with multiple physical morbidities, individuals with a previous record of receiving specialist mental health care, patients residing in the most deprived areas (compared to those living in the least deprived areas), and patients hospitalised in the earlier time period in study (i.e. before 2015). In addition to patient-related factors, this Thesis showed that the intensity of statins prescribed was significantly associated with market supply forces, such as the market entry of lower cost generic atorvastatin in 2012, and further accelerated via health care system demand-side measures, such as clinical guidelines and educational initiatives advocating for the use of higher intensity statin treatment. The overall prescribing budget and the notion of relative cost-effectiveness of different statin types are likely key influencing factors in prescribing decisions.
These findings will be useful to healthcare policy makers and providers in making investment and prioritisation decisions, and underline calls for interventions designed to improve drug initiation and persistence to improve health and curtail rising costs due to preventable vascular events.