Patients Prescribed Warfarin with Poor Time in Therapeutic Range (TTR) Have Different Beliefs about Their Illness and Anticoagulation Therapy Compared to Those with a Good TTR - Early Results from the Switching Study

Medication non-adherence is of increasing concern particularly in management of chronic disease. Lifelong anticoagulation is recommended in patients with atrial fibrillation (AF) and those at risk of recurrent venous thromboembolism (VTE). Anticoagulation control with vitamin-K antagonists (VKAs) is assessed according to TTR, with a TTR>65% indicating good control. Research has shown that patients prescribed VKA with a low TTR (<50%), have worse clinical outcomes and their poor control may relate to low medication adherence. In the UK, the National Institute for Health and Care Excellence recommends that those with a TTR<65% should be considered for direct oral anticoagulants (DOAC) therapy. DOACs have been shown to have less inter-patient variability compared to VKA therapy, meaning that they can be prescribed at fixed doses with minimal monitoring and clinic follow-up. Currently little is known about illness perceptions and medicines beliefs in those prescribed long term anticoagulation with a VKA and how these differ amongst patients with good anticoagulation control (TTR>75%) and those with poor anticoagulation control (TTR<50%). Considering both medication beliefs and illness perceptions have been found to be predictive of adherence in other chronic diseases, the impact of these beliefs on adherence to anticoagulants may be significant if patients with poor VKA control are to be switched to a DOAC, as is recommended.

The Switching study comprises a series of studies investigating illness perceptions and medicines beliefs in those prescribed chronic anticoagulation therapy. We report early results from the first sub-study: This sub-study compares patient beliefs in those with TTR<50% to those with TTR>75% prescribed VKA, to determine if illness perceptions and/or medication beliefs are associated with anticoagulation control and adherence with VKA.

Patients were identified and recruited from the DAWN® databases of the two anticoagulation clinics within King's College Hospital (UK). Eligible patients were administered a questionnaire pack comprised of validated instruments; the revised illness perceptions questionnaire (IPQ-R), the beliefs about medicines questionnaire (BMQ) and the anti-clot treatment scale (ACTS), to assess patients beliefs about their illness, their medicines and their anticoagulation related quality of life. Patients with a TTR>75% were mailed the questionnaire packs. Those with TTR<50% were invited to a pharmacist-led clinic to discuss their anticoagulation and were administered the questionnaire at the point of switching to a DOAC. Completed questionnaires were computed and individual sub-scales analysed using non-parametric tests.

To date, 71 patients with TTR>75% and 77 patients with TTR<50% have been recruited. Median age in the TTR>75% group was 73, with 65% diagnosed with AF and 63% were male. Median age in the TTR<50% group was 68, with 73% diagnosed with AF and 66% were male. Patients with TTR>75%, compared to those with TTR<50%, had lower levels of concerns about VKA (p<0.001) and higher perceptions of the necessity of taking it (p=0.005). The <50% TTR group found VKAs more burdensome (p<0.001) but no difference was found between groups regarding benefits of therapy. The TTR<50% group were more likely to perceive their condition as being acute in duration (p=0.012), cyclical in nature (p=0.003) with more severe consequences (p=0.007) and experienced greater emotional distress relating to their condition (p=0.004). Post-hoc analysis according to indication revealed differences in beliefs between the two groups was driven by the AF cohort. Furthermore, AF patients with TTR<50% were more likely to believe medicines were overused (p=0.027) and harmful (p=0.029) whilst being less likely to believe VKAs are beneficial (p=0.048) with less coherent beliefs regarding their illness (p=0.042) compared to the TTR>75% group.

Our early results demonstrate that AF patients with good INR control have a distinct pattern of beliefs compared to those with poor control. This provides scope for anticoagulation services to target specific beliefs in those with poor anticoagulation control to improve adherence in those requiring long-term anticoagulation in AF. This is of particular importance if this sub-set of patients is likely to be prescribed DOACs where patients are not routinely engaged by services.