Measuring Hydroxychloroquine Levels Helps to Identify Nonadherence
Nonadherence with hydroxychloroquine is a common problem[5,7–10] of which most rheumatologists are unaware.[11,12] In the US Medicaid population followed for 1 year after initiation of hydroxychloroquine, 36% of patients were persistently and 47% of were partially nonadherent (hydroxychloroquine use <80% days/month). Adherence declined over the course of a year.
Although there is no established threshold level to define nonadherence, less than 200 ng/ml has been most frequently utilized in the literature.[5,12] This value is affected by the use of different assays and may not be the appropriate cutoff for all laboratories. Blanchet et al. suggested a serum hydroxychloroquine level of 106 ng/ml. Because of individual differences in metabolism, extremely low levels are most reliable indicators of nonadherence. Several studies have found that use of hydroxychloroquine levels to identify nonadherence and resulting physician–patient discussions improved patient adherence.[12,13–15] Additionally, questionnaires to assess for noncompliance have poorly correlated with blood levels. In one study, 43% of the patients who were nonadherent when detected by drug levels would have qualified as being adherent based on the questionnaire.
Curr Opin Rheumatol. 2022;34(3):151-157. © 2022 Lippincott Williams & Wilkins