Proportion of Days Covered (PDC) is a method used to quantify medication adherence over a defined period. It is calculated by determining the number of days within the period that a patient possesses the medication, divided by the total number of days in that period. For instance, if a patient has a prescription filled for a 90-day supply of medication and refills it precisely on time for a one-year period, the PDC would be 1.0, indicating perfect adherence. A PDC of 0.8 or higher is often considered the threshold for acceptable adherence.
The evaluation of medication-taking behavior is vital for optimizing therapeutic outcomes and managing healthcare costs. Understanding how consistently patients take their prescribed medications allows healthcare providers to identify those who may be at risk for treatment failure or adverse health events. This metric provides a standardized, objective way to assess adherence across various populations and medications, facilitating research and quality improvement initiatives. Historically, methods for assessing adherence were often subjective, relying on patient self-reports. The development of claims data analysis, including PDC calculation, offered a more reliable and readily accessible means of monitoring medication use.
