Riboflavin as an independent and accurate biomarker for adherence in a randomized double-blind and placebo-controlled clinical trial.

Background: Medication adherence is critical for success of clinical trials.

Objective: To assess oral riboflavin is an adherence marker.

Methods: Riboflavin was incorporated into active treatment and placebo pills for a clinical trial lasting for 2 years.

Results: The accuracy (area under the receiver operating curve) of urinary riboflavin was 0.91 as a binary classifier of adherence, and was similar or better than for two active study ingredients daidzein (0.92) and genistein (0.87) (all p < 0.0001). Decreased adherence over time was similar in the two study groups.

Conclusion: Riboflavin is an accurate and useful biomarker for study pill ingestion.