Current Vascular Pharmacology      Send Orders for Reprints to reprints@benthamscience.net 352 Current Vascular Pharmacology, 2019, 17, 352-353 CORRESPONDENCE SECTION Response on Patient Adherence to Novel Oral Anticoagulants (NOACs) for the Treatment of Atrial Fibrillation and Occurrence of Associated Bleed- ing Events: A Systematic Review and Meta-analysis Abdulla Shehab 1,* , Akshaya S. Bhagavathula 1 , Tamrat B. Abebe 2,3 , Tadessa M. Abegaz 2 , Asim A. Elnour 4 , Hani M. Sabbour 5 , Masood Uzzafer 6 , Hersi Ahmad 7 and Adel K. Hamad 8 1 Department of Internal Medicine, United Arab Emirates University, College of Medicine and Health Sciences, Al Ain, UAE; 2 Department of Clinical Pharmacy, University of Gondar - College of Medicine and Health Sciences, Gondar, Ethiopia; 3 Master's Student, Depart- ment of Learning, Informatics, Management and Ethics (LIME), Karolinska Institute, Solna, Sweden; 4 Department of Pharmacy Practice, Pharmacy College, Gulf Medical University, Ajman, UAE; 5 Department of Cardiology, Brown University Warren Alpert School of Medicine, Rhode Island, USA; 6 Health Informatics Consultant, Dallas, Texas, USA; 7 Department of Cardiac Sciences, King Saud University, College of Medicine, Riyadh, KSA; 8 Mohammed bin Khalifa Al Khalifa Cardiac Centre, Bahrain Defence Force Hospital, Ar- Rifaa, Bahrain Dear Editor, We thank Albert and colleagues [1] for their comments and questions. We [2] conducted a literature review which included the terms such as ‘adherence,’ ‘novel oral anticoagulants,’ ‘atrial fibrillation’ and associated ‘bleeding events.’ All in all, the search strings entered in PubMed were: ‘adherence’, ‘com- pliance’, ‘persistence’, ‘atrial’ ‘fibrillation’, ‘treatment’, ‘preferences’, ‘atrial fibrillation’, ‘novel oral anticoagulants’ or ‘oral anticoagulants’ and ‘bleeding events’. ‘Adherence and treatment,’ ‘adherence,’ ‘compliance,’ ‘dabigatran’ or ‘Pradaxa,’ ‘atrial’, fibrillation’, ‘bleeding’, ‘nonvalvular’, ‘stroke’, ‘prevention’, ‘capacitance’ ‘cardiac,’ and ‘antico- agulation.’ ‘Rivaroxaban’ or ‘Xarelto’, ‘treatment’, ‘stroke’, ‘prevention’, ‘adherence’, ‘bleeding’, ‘atrial’, ‘fibrillation’, ‘bleeding’, ‘nonvalvular’ ‘cardiac’ and ‘anticoagulation’. ‘Apixaban’ or ‘Eliquis’, ‘treatment’, ‘stroke’, ‘prevention’, ‘adherence’, ‘bleeding’, ‘atrial’, ‘fibrillation’, ‘compliance’, ‘cardiac’, ‘events’, and ‘anticoagulation’. ‘Edoxaban’, or ‘Savaysa’, ‘treatment’, ‘stroke’, ‘prevention’, ‘adherence’, ‘compliance’, ‘bleeding’, ‘events’, ‘atrial fibrillation’, ‘non- valvular’, ‘preference’, ‘cardiac’ and anticoagulation’. ‘AF’, ‘NVAF’, ‘warfarin’, ‘Coumadin’, ‘direct oral anticoagu- lants’, ‘NOAC’, ‘dabigatran’, ‘rivaroxaban’, ‘apixaban’, ‘edoxaban’, ‘real world’, ‘observational’ and ‘cohort’. Manual searches of reference lists and table of contents of relevant journals were also performed. However, terms *Address correspondence to this author at the Department of Internal Medicine, United Arab Emirates University, College of Medicine and Health Sciences, Al Ain, UAE; Tel: +971-502430220; E-mail: a.shehab@uaeu.ac.ae such as ‘Lixiana’ ‘associated bleeding events’, and ‘DOAC’ were not identified as MeSH terms. Furthermore, our meta- analysis [2] is focused only on observational studies that were published from September 2010 to June 2016. We re- ported heterogeneity and detailed this in the limitation sec- tion. Due to the limited number of studies, we did not per- form a sensitivity analysis or adjust for any confounding that may have a potential influence on outcomes. The International Society for Pharmacoeconomics and Outcome Research (ISPOR) Medication Compliance and Persistence Work Group defines medication adherence as ‘the extent to which a patient acts in accordance with the prescribed interval and dose of dosing regimen’ [3]. In real- world situations, medication adherence measured using claims data has been used for a variety of purposes including the impact of medication non-adherence on clinical out- comes [4]. For example, Woltmann and colleagues evaluated the importance of a commonly used adherence measure (Medication possession ratio- MPR or the proportions of days covered- PDC) as a screening tool to identify patient need for assistance with medication adherence [5]. It is also notable that medication adherence using a retrospective da- tabase, continuous data should not be converted into catego- ries unless empirical evidence exists for a cut-off value. Un- fortunately, no threshold values are yet available for chronic diseases conditions of clinical importance, and thus it is dif- ficult to identify an optimal adherence cut-off point that has been empirically validated [6, 7]. Furthermore, differences in operationalized measures, vocabulary choice, and different interpretations make it difficult to generalize the studies. The new conceptual taxonomy [8] referred by Albert and col- leagues is still under experimental investigations and is not yet widely accepted. A R T I C L E H I S T O R Y Received: June 14, 2018 Revised: June 30, 2018 Accepted: July 02, 2018 DOI: 10.2174/1570161117999190429124137 1875-6212/19 $58.00+.00 © 2019 Bentham Science Publishers