Medication adherence in resistant hypertension: An investigation of prevalence, psychological predictors and patient perspectives

Abstract

Background: Resistant hypertension is a chronic condition in which the arterial blood pressure remains persistently above goal despite concurrent treatment with three or more antihypertensive agents of different classes. It appears relatively common in clinical practice, despite the established effectiveness of antihypertensive medications. Clinical factors such as inadequate dosing of antihypertensive medications, white coat hypertension (the phenomenon in which blood pressure is higher in clinical settings versus other settings), improper blood pressure measurement, and poor adherence to antihypertensive treatment all preclude a diagnosis of resistant hypertension. Poor adherence is considered the most common cause of pseudo-resistance to treatment among patients with apparent treatment-resistant hypertension and can result in unnecessary treatment escalation and referral to specialist hypertension clinics at significant cost to the patient and the healthcare system. Despite forming a core component of the definition and diagnosis of resistant hypertension, the extent, predictors and patient perspectives of non-adherence have not been extensively examined for this group. Aim: The aim of this research is to examine the extent, theoretical predictors, and patient perspectives of non-adherence to antihypertensive medications for apparent treatment-resistant hypertension in primary care. Methods: This research comprised: (1) a systematic review and meta-analysis to examine the extent of medication non-adherence in the published literature, and the study-level predictors thereof; (2) a quantitative cross-sectional study to examine the extent of poor adherence among a large sample of patients with apparent treatment-resistant hypertension receiving treatment in primary care using multiple diverse adherence measures, as well as the predictive value of theoretical constructs drawn from the Common-Sense Model of Self-Regulation (i.e., treatment-favourable beliefs, coherence of beliefs resulting from experience with treatment, and medication-taking habit strength); and (3) a qualitative comparison of high and low adherers to delineate factors associated with good and poor adherence using thematic analysis. Findings: (1) The systematic review and meta-analysis revealed that approximately one-third of patients classed as having apparent treatment-resistant hypertension in the published literature may be more appropriately classed as pseudo-resistant due to poor adherence. Subgroup analysis further revealed that adherence estimates were dependent on the type of adherence assessment method used, with the highest non-adherence observed for physical tests for medications in bodily fluids. There was a small but significant difference in adherence estimates across study settings, with lowest non-adherence estimates observed in primary care settings, suggesting that a proportion of patients may be prematurely referred for specialist treatment without adequate assessment of adherence in primary care. (2) The cross-sectional quantitative study indicated that, even among a single sample of participants, the measure used to assess adherence has a considerable impact on the adherence estimates obtained. Habit strength was demonstrated to be the strongest predictor of adherence behaviour across all analyses. Treatment-related beliefs and coherence of beliefs did not predict adherence, even for patients with relatively weak habits. Treatment burden was also not associated with adherence or habit strength for this sample. (3) The qualitative comparison of high and low adherers identified that illness- and treatment-related beliefs, coherence of beliefs, and medication-taking habits are all important factors in determining whether a patient will adhere to treatment. Most patients described the important role of the general practitioner in promoting good adherence, but highlighted system-related factors as potentially diminishing people’s confidence in their care. Overall differences between high and low adherers were subtly nuanced, highlighting the challenges for healthcare practitioners in clearly identifying poor adherence and potential determinants. Conclusion: The findings of this research provide important new insights into adherence among patients with apparent treatment-resistant hypertension. The quantification of the problem of non-adherence and identification of methodological limitations in the existing literature, quantitative examination of theoretical predictors of adherence, and qualitative investigation into characteristics of high and low adherers with apparent treatment-resistant hypertension together contribute to the evidence base for the development of targeted behavioural interventions to promote antihypertensive adherence in primary care.