Abstract 5961: Defining An Evidence-Based Cutpoint for Medication Adherence in Heart Failure
Patients with heart failure (HF) are required to take multiple medications. Long-term adherence to the HF medication regimen is necessary in order to achieve better patient outcomes. Despite the importance of adherence, clinically relevant cutpoints for distinguishing the level of adherence associated with outcomes are unknown. The purpose of this study was to use outcomes (i.e., event-free) as a criterion to determine the level of medication adherence required to achieve the best clinical outcomes. The specific aim was to determine the cutpoint above which there is a positive relationship between level of medication adherence and outcomes. This was a longitudinal study of 135 patients with HF. Medication adherence was measured using a valid and objective measure, the Medication Event Monitoring System (MEMS). Two indicators of adherence were assessed by the MEMS:
dose-count, percentage of prescribed doses taken and
dose-days, percentage of days correct number of doses taken. Patients were followed up to 3.5 years to collect data on outcomes.
A series of Kaplan-Meier plots with log-rank tests, Cox-survival analyses, and receiver operating characteristic (ROC) curves were assessed comparing event-free survival in patients divided at one point incremental cutpoints. Event-free survival was significantly better when the prescribed number of doses taken [dose-count] or the correct dose [dose-day]) was ≥ 88%. This level was confirmed in a Cox regression model controlling for age, gender, ejection fraction, NYHA, comorbidity, angiotensin-converting enzyme inhibitor use, and beta-blocker use. ROC curves showed that adherence rates above 88 – 89% produced the optimal combination of sensitivity and specificity with respect to predicting better event-free survival. With this as the adherence cutpoint, patients in the nonadherent group were 2.2 times (by dose-count) to 3.2 times (by dose-day) more likely to experience a first event (p= .021 and .002, respectively), compared to patients in the adherent group. The results of this study provide clinicians and researchers with an evidence-based recommendation about the level of adherence needed to achieve the best outcomes.