P609A systematic review of adherence to preventative low-dose aspirin therapy and its effects on ischaemic vascular outcomes

Background: Low-dose aspirin is effective in the prevention of ischemic vascular events and colorectal cancer (CRC); however, adherence to therapy is likely an important factor for these benefits to be seen. A comprehensive update of randomized controlled trials (RCTs) and observational studies regarding adherence to low-dose aspirin has not been previously published. Purpose: To systematically review the literature regarding adherence to low-dose aspirin therapy (≤325 mg/day). Methods: PubMed and Embase databases were searched (up to June 2016) to identify randomized controlled trials (RCTs) and observational studies that reported adherence or discontinuation rates to low-dose aspirin and/or effects of low-dose aspirin adherence/discontinuation on cardio/cerebro-vascular disease (CVD/CeVD) risk. Potential articles were screened by two independent reviewers; bibliographies of identified articles were reviewed to identify further relevant studies. Results: Seventy nine studies were included: 22 RCTs, 51 observational studies and 6 reviews. Distribution of the 73 original studies by geographical area is depicted in the Figure. Among RCTs, adherence ranged from 72.5% to 85.7% among primary cardio/cerebro-vascular disease (CVD/CeVD) prevention populations and 69% to 88% among secondary CVD/CeVD prevention populations. Among observational studies, the majority of adherence estimates were >80% at 2 years; discontinuation estimates were <10% at 1 year, 20–35% at 2 years and <65% for 3–5 years. Twenty two studies (4 RCTs; 18 observational studies) compared CVD/CeVD risk between patients who were adherent/persistent to low-dose aspirin compared to non-adherers/discontinuers; 21 (4 in primary prevention populations, 15 in secondary prevention populations and 2 in both) found adherers had significantly reduced risks of at least one CVD/CeVD event type; one study found no association. One large RCT of men without previous myocardial infarction (MI), reported a 51% reduction in MI risk for adherers (p<0.0001). Of 12/22 studies that reported effects of discontinuation, low-dose aspirin was significantly associated with an increased risk of at least one type of CVD/CeVD outcome in 11/12 studies.