Heart failure is a serious, chronic condition that requires lifelong, strict adherence to medication regimens. Nonadherence increases morbidity and mortality rates as well as associated health care costs. Wu and colleagues sought to determine the medication adherence level associated with better outcomes in a prospective, longitudinal study of 135 patients with heart failure. The primary composite outcome was time to any of the following: ED visit for worsened heart failure, cardiac rehospitalization, or death from any cause. Medication adherence was measured using the Medication Event Monitoring System, which considers two indicators of adherence: dose count (the percentage of prescribed doses taken) and dose day (the percentage of days the correct number of prescribed doses was taken). Patients were followed for three and a half years.

The results indicated that health outcomes were significantly better when dose count or dose day was at or above 88%. Achievement of this adherence level translates to taking 53 of 60 doses of a drug prescribed at twice a day for 30 days (dose count) and these doses must be taken correctly on at least 26 days (dose day). These results provide clinicians with the first evidence-based level of adherence to medication necessary to achieve lower rates of ED visits, cardiac rehospitalizations, and death in patients with congestive heart failure. According to lead author Wu, "Nurses need to inform their heart failure patients that only a high level of adherence to their chronic medication regimen will produce positive outcomes."