OBJECTIVE: To identify various types of non-adherence among users of antihypertensive medications by establishing components of adherence measures and use these components for measuring the prevalence of non-adherence.
SETTING: Twelve community pharmacies from the Danish county of Funen.
METHOD: Users of antihypertensive medication were included in the study. 2,914 medication users received questionnaires by mail. Participating patients were asked to fill in two questionnaire regarding demographics, self-reported blood pressure, and various adherence measures. Two factor analyses were conducted based on responses to questions.
MAIN OUTCOME MEASURES: Medication-taking behaviour and self-efficacy (beliefs about ability and capacity to accomplish a task), respectively. Other measures of non-adherence collected by questionnaire were also addressed in the data for comparison of prevalence with the developed concepts.
RESULTS: 1,426 (49%) participants answered the questionnaires. The analyses resulted in two sets of components: three adherence behaviour measures and two self-efficacy measures which showed similarities in concepts. The adherence behaviour measures included two concepts of intentional nonadherence (associated with aspects of self-regulation and effect concerns, respectively) and one measure of non-intentional non-adherence. Prevalence of the developed measures of behaviour related non-adherence ranged from 10.3 to 34.9% depending on which type of non-adherence measure was used. Established measures of non-adherence resulted in prevalence between 2.2 and 39.6%.
CONCLUSIONS: The study showed that concepts of non-adherence measurements could be determined including self-efficacy aspects, unintentional non-adherence and intentional non-adherence related to self-regulation and effect concerns respectively. The prevalence of the adherence behaviour components were found to be between 10.3 and 34.9%, which is in the range of expected values. Associations between the new concepts of non-adherence measurement and characteristics of nonadherers remain to be established and would be a subject for further studies.