Pos0531 Therapeutic Hydroxychloroquine Blood Levels Predict Lower Mean Frequency of Acute Care Utilization in Lupus

Background: Up to 80% of patients with lupus (or SLE) are nonadherent to hydroxychloroquine (HCQ) associated with 45% higher acute care visits. HCQ nonadherence is even higher in patients of Black race or those with social barriers, potentially leading to higher acute care use and poor outcomes. Moreover, recent studies showed that the recommended HCQ dose (≤5 mg/kg/day) risk 6-fold higher SLE flares requiring hospitalization, due to subtherapeutic HCQ levels. Therefore, therapeutic drug level monitoring for HCQ in blood could guide clinicians to optimize HCQ dosing to maximize efficacy, adherence, and reduce acute care visits. Yet, HCQ blood level monitoring is not routinely done in North America due to concerns about cost and coverage. Establishing that HCQ blood level monitoring could reduce healthcare costs, acute care use, and improve outcomes in lupus would support payer approval to monitor HCQ levels during routine SLE visits. Objectives: The objective of this study was to examine the effectiveness of HCQ blood level monitoring in reducing the risk of acute care visits in patients with vs. without therapeutic HCQ blood levels. Methods: We measured HCQ blood levels during 223 consecutive patient-visits using liquid chromatography mass spectrometry. HCQ blood levels were categorized as: a) subtherapeutic (1200 ng/ml) per our prior findings 1. All lupus-related acute care (hospital or ER) visits from the index patient visit through the next follow-up visit were manually abstracted. Covariates included socio-demographics, SLE disease activity score, SLE damage index, kidney function, steroid and HCQ doses, history of previous SLE related acute care visits, exposure to SLE triggers (e.g., infection), or immunosuppressive drugs. Using Proportional Means Hazards modelling, we examined associations between HCQ blood levels and acute care visits including recurrent visits. Using the results of our Proportional Means Hazards model, we calculated the predicted mean frequency of acute care visits with therapeutic HCQ levels stratified by race adjusting for covariates. Results: Across 223 patient-visits, a total of 39 SLE-related acute care visits were observed. We noted that patients of Black race or Hispanic ethnicity had 4-fold higher risk of acute care visits (Adjusted HR 3.8; Table 1). A recent exposure to SLE triggers, higher steroid doses, and previous SLE-related acute care visits were was associated with higher acute care visits (Table 1). Finally, a 78% lower risk of acute care visits was seen in patients with therapeutic HCQ blood levels, 750-1200 ng/ml, compared to those with subtherapeutic levels, Conclusion: Therapeutic HCQ blood levels (750-1200 ng/ml) were associated with 78% lower acute care visits, and predicted 5x lower acute care visits in patients of Black race or Hispanic ethnicity who historically face higher nonadherence and worse SLE outcomes. Therapeutic HCQ blood level monitoring could prevent unnecessary acute care visits and health disparities in lupus, thus warranting its use during SLE visits. REFERENCES: 1 Garg, S., Chewning, B., Hutson, P., Astor, B.C. and Bartels, C.M. (2024), Reference Range of Hydroxychloroquine Blood Levels That Can Reduce Odds of Active Lupus and Prevent Flares. Arthritis Care Res. https://doi.org/10.1002/acr.25228 Acknowledgements: The UW SLE Cohort is supported by the Department of Medicine and the Institute for Clinical and Translational Research at the University of Wisconsin-Madison. Disclosure of Interests: None declared.