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

Background: Assessment 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.

Purpose: To 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.