Discussion
This study confirms that non-adherence in patients on DOACs is prevalent
with non-adherence scores of 9% (range 3-33% depending on the used
cut-off value for discriminating between adherence and non-adherence).
The non-adherence score of 33% for the cut-off value of <25
seems to be even higher than the 21% found in the study by Capiau et al
using the same <25 cut-off score [7] and being comparable
with the estimated adherence of 69% (i.e. 31% non-adherence) that was
found in the meta-analysis by Ozaki et al. [10] that we used for our
power analysis. We found associations between adherence and both side
effects and side effect burden, regardless of the MARS-5 cut-off value.
Bruising and minor bleeds were the most reported side effects by far.
This is in line with the results reported in the cited studies in the
introduction of Toorop et al. and Mitrovic et al. [8,12,13].
However, this finding contrasts with the most reported side effects in
the Lareb Intensive Monitoring (LIM) study conducted by Rolfes et al.
where dizziness, tiredness and headaches made up the top three [13].
Although previous studies demonstrated that high BMQ-necessity and low
BMQ-concern beliefs are considered to be associated with medication
adherence, this study did not found an association between patient’s
beliefs about DOACs and adherence. This is not surprising as all
included patients showed higher necessity scores compared to other
studies, resulting in less contrast in the study population. We found
both a higher mean BMQ-necessity score and a higher BMQ-concerns score
compared to Capiau et el. (21 vs 16 and 16 vs 10, respectively) [6].
For the primary cut-off value all patients in the non-adherence group
scored high on necessity beliefs, meaning that patients’ knowing of the
importance of proper DOAC use (knowledge) does not suffice for good
adherence (behavior).
We found that non-adherent patients, patients reporting side effects
related to their DOAC use and patients experiencing a high side effect
burden all more often believed that DOACs have unpleasant side effects
(BMQ question 11). Side effects were associated with non-adherence even
in patients having high necessity beliefs. This means that both the
occurrence of side effects, the side effect burden (experiential aspect)
and concern beliefs about side effects (cognitive aspect) are associated
with non-adherence.
No associations were found between adherence and either gender,
indication, DOAC and dosage. It is noteworthy however that for the
primary cut-off score all non-adherent patients were on DOAC therapy for
the indication atrial fibrillation. One could speculate that patients
with atrial fibrillation without a history of ischemic stroke that need
to use a DOAC to prevent future thromboembolic events are less motivated
for and prone to proper adherence than people that have suffered from
deep vein thrombosis and pulmonary embolism.