Objective: (i) To obtain an overview of measured compliance with antihypertensive medication; (ii) to explore sources of variation in measured compliance percentages between studies; and (iii) to investigate whether studies can establish a relationship between compliance and achieved blood pressure.
Study selection: MEDLINE, PubMed and EMBASE databases were searched for studies, published between 1985 and 2003, in which patient compliance with antihypertensive medication was measured with electronic monitors.
Data extraction: A standard form was used to extract relevant data from the included articles. Two investigators extracted all data independently.
Results: Thirty studies were identified. The studies included were highly varied in their methods used to quantify compliance. Taking compliance and/or correct dosing were used in 20 studies. Mean taking compliance for a once-daily regimen was 94.0 +/- 4.4% and 88.2 +/- 6.5% for a twice-daily regimen. Mean correct dosing was 85.0 +/- 8.7% for a once-daily regimen and 75.3 +/- 6.5% for a twice-daily regimen. Proportions of patients with taking compliance or correct dosing </= 80% were provided by only five studies and ranged between 9 and 37%. Studies with a monitoring period exceeding 6 months showed a distinct decrease in compliance over time. Studies on the association between achieved blood pressure and compliance gave inconsistent results.
Conclusions: Although poor compliance is assumed to be an important explanation for inadequate blood pressure control, any convincing empirical evidence to support this hypothesis is currently lacking. The relationship between patient compliance and blood pressure control has not yet been properly established.