Abstract
HCQ is a cornerstone therapy for SLE, offering critical benefits in disease management, including improved survival, reduced flare risks and decreased organ damage. Significant variability in HCQ blood levels among patients challenges the efficacy of traditional weight-based dosing and highlights the need for individualized treatment strategies. We conducted a comprehensive review of peer-reviewed studies across multiple databases to synthesize current evidence on factors influencing HCQ pharmacokinetics, optimal timing and frequency of testing, matrix selection and interpretation of results. While further research is needed to refine HCQ monitoring strategies, this review summarizes the most up-to-date evidence. HCQ blood concentrations may be influenced by patient weight, kidney function and cytochrome P450 genetic polymorphisms. Whole blood is the preferred matrix for measurement, offering greater accuracy than serum or plasma. Testing should be performed no earlier than 6 months after treatment initiation, with trough levels being ideal, though random levels remain acceptable in clinical practice. Whole blood concentrations <200 ng/ml indicate severe nonadherence, while levels between 200 and 750 ng/ml suggest partial nonadherence. A therapeutic target range of 750-1200 ng/ml is associated with improved disease control, and levels >1200 ng/ml may increase the risk of retinal toxicity.