The purposes of this dissertation were to (1) determine which indicators of medication adherence are effective predictors of emergency department (ED) visits, rehospitalization, and mortality, and (2) explore factors contributing to medication adherence in patients with heart failure (HF). Two systematic reviews and three research studies were conducted for these purposes. In the first review, literature on factors affecting medication adherence was summarized. In the second review, three methods (i.e., self-report, pharma4 refill, and Medication Event Monitoring System) of measuring medication adherence were compared. The first research study was a qualitative descriptive study exploring factors influencing medication adherence in 16 HF patients. The second study was a psychometric evaluation of the Medication Adherence Scale (MAS), designed to measure patients' attitudes toward, knowledge of, and barriers to medication adherence. The third study was a longitudinal study to (1) determine which indicators of medication adherence effectively predicted health outcomes, and (2) explore sociodemographic, clinical, and psychosocial variables that contribute to medication adherence in HF patients.
The reviews of the literature demonstrated that patients are often non-adherent to medication taking, that a wide range of factors contribute to nonadherence, and that the most valid measure of medication adherence in a research setting is the objective Medication Event Monitoring System (MEMS). From the qualitative study, patients identified facilitators and barriers to medication adherence. The psychometric study demonstrated that the MAS is a reliable and valid instrument for measuring patients' attitudes, knowledge, and barriers related to medication adherence. In the final research study, medication adherence, measured using the MEMS, predicted event-free survival. The most influential variable associated with medication adherence was patient perceived barriers to medication adherence. Minorities and those who had more severe symptoms, less income, and less social support also are at high risk for medication nonadherence. The findings from this dissertation provide evidence of the important impact of medication adherence on clinical outcomes, and provide clinicians and researchers a basis for effective interventions to improve medication adherence and in turn clinical outcomes in patients with HF.
Keywords: Medication Adherence, Heart Failure, Model Testing, Rehospitalization, Mortality.
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