Precision HCQ Dosing Personalizes Lupus Care

Hydroxychloroquine (HCQ) is the cornerstone of systemic lupus erythematosus (SLE) pharmacotherapy, prescribed lifelong to reduce flares, organ damage accrual, and mortality. Yet for decades, dosing has been governed by a one-size-fits-all framework that does not account for the individual variation in drug absorption, renal elimination, and metabolism that shapes how much active drug actually reaches the sites of inflammation.

Changing that, Shivani Garg, MD, PhD, argues, requires the same precision dosing revolution that transformed oncology — applied now to lupus, where the therapeutic stakes of getting the dose wrong play out over years and decades.

RheumatologyLive sat down for a recent interview with Garg, who is an associate professor in the Section of Rheumatology, Allergy, and Immunology at Yale School of Medicine in New Haven, Connecticut, where she serves as director of the Yale Lupus Clinical Research Program and co-director of the Yale Lupus Program. During Lupus Awareness Month, she spoke about the conceptual and clinical foundation for this work — and where the field needs to go next.

Current weight-based HCQ dosing, capped at 5 mg/kg/day per current guidelines, represents a meaningful improvement over earlier fixed-dose regimens, but it still leaves critical sources of interindividual variability unaddressed. Kidney function alters HCQ clearance substantially — Garg's work has demonstrated that even modest reductions in eGFR, beginning at stage 2B chronic kidney disease (eGFR 60–75 mL/min/1.73 m²), are associated with higher HCQ blood levels, with implications for both retinopathy risk and dose calibration that weight-based dosing cannot capture.¹ Drug interactions, metabolic polymorphisms that determine whether a patient is a fast or slow metabolizer, and gastrointestinal absorption variability compound this further. The practical consequence is that 2 patients with identical body weight and prescribed doses can have meaningfully different blood HCQ concentrations and, downstream, meaningfully different probabilities of disease control and toxicity.

The therapeutic reference range Garg and colleagues defined — 750 to 1150 ng/mL in whole blood — represents the first empirically derived target for HCQ monitoring in SLE. Published in Arthritis & Rheumatology in 2026 using data from the international SLICC cohort, the analysis found that patients within this range demonstrated the greatest reduction in odds of active lupus; patients above 1150 ng/mL accrued no additional efficacy benefit but faced increasing retinopathy risk, while patients below 750 ng/mL were subtherapeutically exposed.¹ An earlier cohort study from Garg's group, published in Arthritis Care & Research, found that maintaining HCQ levels within the therapeutic range was associated with a 26% reduction in odds of flares over 9 months of follow-up. A companion real-world longitudinal study published in Arthritis Care & Research in 2026 extended these findings prospectively, demonstrating that blood level monitoring — applied in clinical practice to guide dose adjustment — translated into measurable improvements in lupus outcomes over time.²

Garg situated this work within the broader arc of precision medicine, drawing a direct parallel to the oncology experience: tumor biopsy–guided, mutation-targeted therapy fundamentally changed cancer outcomes not because new drugs were invented in isolation, but because the dosing and patient selection frameworks were rebuilt around individual biology. The translational pathway for lupus is analogous — with HCQ serving as the proof-of-concept target because of its ubiquitous use, long duration of administration, and the availability of validated blood level assays.

The issue of adherence has particular salience. HCQ-associated retinopathy — a serious but uncommon complication that can affect color vision and peripheral visual fields — represents the toxicity patients fear most, and fear of it frequently leads patients to reduce or discontinue a medication that is otherwise reducing their risk of flare, hospitalization, and damage accrual. Garg described blood level monitoring as a tool not only for dose optimization but for patient communication: showing a patient that their HCQ level falls within the established therapeutic range — not supratherapeutic and not approaching retinopathy risk thresholds — provides objective reassurance that can support long-term adherence and shared decision-making.

Looking forward, Garg described target-site pharmacokinetics — the question of how much drug from the systemic circulation actually penetrates to the tissue compartment where inflammation is occurring — as the next research frontier. Blood levels reflect systemic drug availability but may not capture the full picture for organ-specific manifestations such as cutaneous lupus or lupus nephritis, where inflammation occurs in tissue compartments with distinct pharmacokinetic properties. Building integrated pharmacokinetic-pharmacodynamic models that link blood levels to target-site drug concentrations and, ultimately, to molecular immune pathway activity represents the longer-term vision for precision dosing in lupus and other chronic inflammatory diseases.

“The step up of the target site pharmacokinetics immune integration model is is right now in early stages. So lots more to do, but at one point, if we are able to understand how much the medicine gets into the target site, we might be able to identify better pathways of better formulations, newer medicines, effective formulations. So it all leads to a really interesting path or exciting future for patients with lupus, lupus, nephitis and other chronic diseases,” Garg said.

Editor’s note: Garg’s reported disclosures include NIH, NIAMS, Lupus Foundation of America, Lupus Research Alliance, and Rheumatology Research Foundation.

References

1. Garg S, Blanchet B, Nguyen Y, et al; SLICC Investigators. Defining optimally safe and effective blood levels of hydroxychloroquine in lupus: an important step toward precision drug monitoring. Arthritis Rheumatol. 2026;78:1102-1113. doi:10.1002/art.70010

2. Patel JJ, Hollnagel F, Packee C, Kapoor A, Rovin B, Costedoat-Chalumeau N, Garg S. Real-world longitudinal data on the impact of hydroxychloroquine blood level monitoring on lupus outcomes: results of a prospective longitudinal cohort study. Arthritis Care Res. 2026. doi:10.1002/acr.80059

3. Balevic SJ, Thomas D, Garg S. Toward optimal dosing in SLE: the case for hydroxychloroquine blood level monitoring. Arthritis Care Res. 2026. doi:10.1002/acr.80020