Anticoagulant therapy is prescribed for millions of patient’s world-wide, most commonly for the acute treatment and long-term prevention of venous thromboembolism (VTE) and as primary and secondary prevention of stroke in the context of atrial fibrillation (AF) [
1,
2]. Until recently the majority of patients requiring chronic anticoagulant therapy were prescribed vitamin K antagonists (VKA), as these were the only oral anticoagulant agents available [
1,
2]. VKA therapy comes with some practical disadvantages; need for monitoring and a relatively significant number of drug-drug and drug-food interactions, which has meant that not all patients eligible have benefitted from these agents in the past [
3]. In recent years, the aforementioned disadvantages has led to the development of new classes of oral anticoagulants, the direct thrombin inhibitor (dabigatran) and the direct Xa inhibitors (apixaban, betrixaban, edoxaban, rivaroxaban). These agents hold many advantages over VKA, primarily of a predictable pharmacokinetic nature, meaning that there is minimal requirement for regular monitoring of anticoagulant effect [
4]. In the United Kingdom (UK), the available direct oral anticoagulants, apixaban, dabigatran, edoxaban and rivaroxaban are all approved for AF and VTE indications and available for clinicians to prescribe as treatment options, when clinically indicated [
5‐
13]. Indeed their availability has sparked local initiatives to ensure that patients in AF with a CHA
2DS
2VASc score [
14] of two or above are offered oral anticoagulation, be it with VKA or the novel agents, referred to herein as NOAC. The general perception is, that the NOACs are
easier to use, so uptake both from a clinician (prescribing) and patient (receiving) perspective is likely to be higher, with cost analyses modelling suggesting that these agents are cost-effective [
5‐
13]. Treatment pathways across the UK are being revisited to accommodate these agents and the advantages they bring. However, these agents are not free from risks. Compared to VKA, little experience exists on how these agents perform long-term, e.g. in minimising complications associated with VTE such as the post-thrombotic syndrome. Additionally, there are currently no antidotes available for the direct Xa inhibitors; a situation which is likely to change in the coming months. Finally, the benefits cited for the NOACs assume that patients actually take the medication as prescribed. Research suggests that approximately 30–50 % of medication prescribed for chronic conditions are not taken as intended [
15]; adherence is often found to be high during the initial months of therapy and then found to decline in many patients [
16], with clinician’s ability to recognise medication non-adherence reported to be poor [
17‐
20]. Medication non-adherence not only impacts negatively on the patient concerned, the wider health-care economy is adversely affected [
21]. Research confirms that individual patient’s beliefs about medicines are a strong predictor of their adherence to treatment. These beliefs can be grouped under two categories; (1) perceptions of necessity and (2) concerns about negative effects [
22]. Therefore beliefs that failure to take the treatment could result in adverse consequences is associated with higher adherence rates (and vice versa). Acknowledging that all patients will have differing beliefs about their medications is the first step in addressing the medication non-adherence problem [
22,
23].
With the availability of NOAC therapy, an opportunity now exists to re-visit patients who are currently prescribed VKA with poor anticoagulation control, and consider switching their anticoagulant therapy to a NOAC. The question is how to determine
success or
failure on VKA. A common method of determining good anticoagulation control on VKA is through their time in therapeutic range (TTR). The Rosendaal method [
24] is the most widely used method to calculate TTR and uses linear interpolation to calculate an INR value for each day between observed INR values (over a 1 year period). The TTR represents the percentage of these INR values in days that are in the therapeutic range. The TTR is a valid marker to use in clinic, as it has been reported to predict clinical outcomes such as major bleeding, stroke and systemic embolic events [
25]. TTR provides a means, however imperfect [
26], of identifying possible medication non-adherence and/or whether the patient may benefit from a switch to NOAC. In the UK, national guidelines suggest using the TTR criteria for determining which patients might be prioritised for switching to a NOAC. Indeed, the recently published National Institute for Care Excellence guidelines for AF stipulate that anticoagulation clinics should reassess anticoagulation for patients with poor anticoagulation control, and one of the criterion specified for re-assessment is if a patient’s TTR is <65 % [
27].
Non-adherence in the context of anticoagulant therapy is not new and the issue has received attention from researchers in the past [
28‐
32], with the importance of non-adherence to NOAC now emerging [
33‐
35]. Little research exists on what patients general and specific concerns or necessity might be about the VKA that they are currently prescribed. This is important, as with a significant change in the anticoagulation landscape, understanding the patient perspective, particularly those with poor TTR, could help identify patterns of concerns that this group of patients may have, which could impact on their medication taking behaviour, if switched to a NOAC. Studying this would help with service delivery and determine if a specific clinical pathway would support adherence with chronic anticoagulant therapy in those identified or suspected of poor adherence - as currently, no long term pathway for NOAC patients is expected to be in place.
The Switching study is a series of prospective studies designed to investigate the association between medication adherence and patients’ beliefs about anticoagulation therapy (warfarin and subsequently NOAC) together with beliefs about their illness and anticoagulation-related quality of life.