Prevalence and predictors of medication non-adherence among people living with multimorbidity: a systematic review and meta-analysis
Problem
Risk of non-adherence to treatments increases as people are prescribed more medications. This may have important implications for people living with multimorbidity – the presence of two or more chronic conditions – which is closely associated with polypharmacy. The extent of non-adherence in multimorbidity is poorly understood, attributable to challenges in measuring multiple medication adherence. However, it is recognised that non-adherence can exacerbate the burden experienced by people with multimorbidity through increased morbidity and mortality. Medication adherence can be influenced by many factors, including treatment characteristics, condition-related factors, and illness and medication beliefs. To our knowledge, reported correlates of non-adherence in multimorbidity have not been synthesised. We aimed to determine the prevalence and predictors of medication non-adherence among people living with multimorbidity by conducting a systematic review of the existing literature.
Approach
Four databases were systematically searched for articles published in English between January 2009 and April 2019. Quantitative studies reporting medication non-adherence and/or predictors of non-adherence among people with two or more chronic conditions were included. One reviewer screened all titles and abstracts, with 20% screened by a second reviewer. Full-texts were screened independently by two reviewers. Study quality was appraised using a tool for observational studies previously adapted for the medication adherence literature. Meta-analysis was conducted with a sub-group of studies that used an inclusive definition of multimorbidity to recruit participants, rather than seeking people with specific conditions. Remaining studies were narratively synthesised.
Findings
A total of 11,073 records were identified. Following full-text screening, 177 were included. The range of reported non-adherence differed by measurement method; 76.5% for self-report, 65.6% for pharmacy data and 44.1% for electronic monitoring. A meta-analysis was conducted with 8 studies (n = 8949) that used an inclusive definition of multimorbidity to recruit participants. The pooled prevalence of non-adherence was 42.6% (95% CI = 34.0-51.3%, k = 8, I2 = 97%, p < 0.01). Among studies reporting adherence separately for two or more conditions, the difference in non-adherence between conditions ranged from 0.8% to 33.6%. Eleven studies reported predictors of non-adherence; frequent predictors included previous non-adherence and treatment-related beliefs. Number of chronic conditions was not a consistent predictor of non-adherence.
Consequences
We identified a heterogeneous literature reporting medication non-adherence among people living with multimorbidity. Variation in study design, population, and measurement and definitions of both multimorbidity and non-adherence was observed between studies. Disparities in non-adherence between conditions might be explained by factors such as prioritisation among conditions, regimen complexity, or differences in the expected efficacy of medications. Methods to measure multiple medication adherence are needed to determine the true extent of within-individual differences in non-adherence among people with multimorbidity. Attempts by healthcare providers to improve adherence in this population should involve determining which conditions and medications require most support.