Effectiveness and content analysis of interventions to enhance medication adherence and blood pressure control in hypertension: A systematic review and meta-analysis

OBJECTIVE: The objective of this systematic review is to evaluate the effectiveness of medication adherence interventions on blood pressure control in hypertensive patients. In addition, we aim to explore what barriers and facilitators in the interventions may have been targeted and how these might be related to the effect size on blood pressure (BP). DESIGN: This review is a hypertension-specific update to the previous Cochrane Review by Nieuwlaat et al. ( 2014 ) on interventions to enhance medication adherence. A systematic literature search was carried out and two authors independently screened titles and abstracts for their eligibility for inclusion and independently extracted data from the selected studies and assessed the methodological quality using the Cochrane Collaboration Risk of Bias Tool. A meta-analysis was conducted and additionally, theoretical factors in interventions were identified using the Theoretical Domains Framework. RESULTS: The meta-analysis found a modest main effect of adherence interventions on SBP (MD -2.71 mm Hg, 95% CI -4.17 to -1.26) and DBP (MD -1.25 mm Hg, 95% CI -1.72 to -.79). However, there was substantial significant heterogeneity across both outcomes. A narrative review on adherence outcomes was conducted. In terms of the theoretical analysis, the relationship between the total number of times the domains were coded within an intervention and change of SBP (r  =  -.234, p = .335) and DBP was not significant (r  =  -.080, p = .732). Similarly, the relationship between the total number of times different domains were coded within an intervention and change of SBP (r  =  .080, p = .746) and DBP was not significant (r  =  -.188, p = .415). DISCUSSION: This review and meta-analysis of interventions documented significant but modest post-intervention improvements in BP outcomes among hypertensive patients. However, this is a tentative finding as substantial heterogeneity and potential biases were present. One of the greatest challenges of this review was assessing risk of bias, extracting sufficient data to calculate effect size and coding interventions with the amount of information provided in papers. It is imperative that future adherence research comprehensively reports methodology.