Medication adherence assessment in a clinical trial with centralized follow-up and direct-to-patient drug shipments:

BackgroundAssessment of adherence to study medications is a common challenge in clinical research. Counting unused study medication is the predominant method by which adherence is assessed in outpatient clinical trials but it has limitations that include questionable validity and burdens on research personnel.PurposeTo compare capsule counts, patient questionnaire responses, and plasma drug levels as methods of determining adherence in a clinical trial that had 2056 participants and used centralized drug distribution and patient follow-up.MethodsCapsule counts from study medication bottles returned by participants and responses to questions regarding adherence during quarterly telephone interviews were averaged and compared. Both measures were compared to plasma drug levels obtained at the 3-month study visit of patients in the treatment group. Counts and questionnaire responses were converted to adherence rates (doses taken divided by days elapsed) and were categorized by stringent (≥85.7%) and liberal (...