Up to a third of all strokes are recurrent events, which tend to be more severe and lead to increased levels of disability. Medications to control cardiovascular risk factors, such as hypertension, dyslipidaemia and atrial fibrillation, are essential for secondary prevention. However, medication adherence is often poor, with up to a third of patients failing to take medications as prescribed after a stroke or transient ischaemic attack.1 Cognitive impairment, which can range from mild to severe impairment or dementia, is common after stroke. Cardiovascular risk factors are associated with an increased risk of developing cognitive impairment, as well as increasing the risks of recurrent strokes. Controlling cardiovascular risk factors through the use of secondary prevention medications could therefore reduce the risks of cognitive decline, as well as reducing the risks of recurrent events. Taking medications as prescribed involves several cognitive functions, which may be affected by cognitive impairment. Our recently published research in PLOS One systematically reviewed the association between cognitive impairment and medication non-adherence in patients with stroke.2
We identified nine studies, with substantial differences in study populations, definitions, and assessments of cognitive impairment and medication non-adherence. Measures of cognitive impairment varied from a diagnosis of dementia to a standardised cognitive assessment. Medication adherence was assessed through self-report or the use of administrative databases. Non-adherence was variously defined as non-persistence (discontinuation of medications according to a pre-defined treatment gap), poor self-reported adherence, or poor adherence according to the proportion of days covered by dispensed medications.
The findings of included studies were discordant, with three studies reporting that cognitive impairment was associated with increased medication non-adherence, three studies reporting that cognitive impairment was associated with decreased non-adherence, and three studies reporting no statistically significant associations between cognitive impairment and adherence. While there was no evidence of an association between cognitive impairment and non-adherence when all nine studies were pooled quantitatively, the meta-analysis revealed substantial and significant heterogeneity between studies. The overall quality of the evidence was low, with further research likely to have a significant impact on the reported estimates.
The substantial heterogeneity between studies, coupled with the low evidence quality, makes it difficult to draw definitive conclusions. Medication adherence consists of three phases: initiation, implementation, and discontinuation or non-persistence,3 with adherence more accurately conceptualised as a set of dynamic behaviours occurring within each of these phases, rather than as a unidimensional, static construct.4 Thus, there are many ways in which patients with stroke can be non-adherent, and it is not surprising that the results of studies defining and measuring different aspects of medication adherence at different time points, in different study populations and with different medication regimens, are inconclusive or contradictory. Future studies should therefore explicitly state which adherence behaviour, to which medication, and at which phase in the adherence continuum, is being measured, in order to progress the literature and facilitate the development of feasible, evidence-based interventions to improve adherence.4,5 Considering the importance of secondary prevention and the impact of poor adherence on health outcomes, further research is required to clarify the association between cognitive impairment and medication adherence after stroke, and to identify patients at greatest risk of non-adherence.
SPHeRE programme PhD scholar
Royal College of Surgeons in Ireland
- Al AlShaikh S, Quinn T, Dunn W, Walters M, Dawson J. Predictive factors of non-adherence to secondary preventative medication after stroke or transient ischaemic attack: A systematic review and meta-analyses. European Stroke Journal. 2016.10.1177/2396987316647187.
- Rohde D, Merriman NA, Doyle F, Bennett K, Williams D, Hickey A. Does cognitive impairment impact adherence? A systematic review and meta-analysis of the association between cognitive impairment and medication non-adherence in stroke. PLoS One. 2017;12(12):e0189339.10.1371/journal.pone.0189339.
- Vrijens B, De Geest S, Hughes DA, Przemyslaw K, Demonceau J, Ruppar T, et al. A new taxonomy for describing and defining adherence to medications. Br J Clin Pharmacol. 2012;73(5):691-705.10.1111/j.1365-2125.2012.04167.
- Gellad WF, Thorpe CT, Steiner JF, Voils CI. The myths of medication adherence. Pharmacoepidemiol Drug Saf. 2017;26(12):1437-41.10.1002/pds.4334.
- Molloy GJ, O’Carroll RE. Medication adherence across the lifespan: Theory, methods, interventions and six grand challenges. Psychol Health. 2017;32(10):1169-75.10.1080/08870446.2017.1316850.