Therapeutic Drug Monitoring (TDM) of Hydroxychloroquine in Whole Blood: Analysis of Over 10,000 Patient Results Using Lab Developed Liquid Chromatography Tandem Mass Spectrometry

Hydroxychloroquine (HCQ), a mainstay SLE therapy, improves survival and reduces flares. Therapeutic drug monitoring (TDM) may be useful in 1) identifying and improving adherence issues, 2) titrating daily dose to achieve therapeutic benefits associated with whole blood HCQ >1000 ng/mL while 3) minimizing cumulative exposure by keeping levels <2000 ng/mL. Whole blood (WB) is the correct specimen because WB HCQ levels are higher than serum or plasma levels, more stable and reflective of the last month of HCQ ingestion, and are better correlated to efficacy and retinopathy risk.