HealthDay News – For patients with systemic lupus erythematosus (SLE), lower hydroxychloroquine (HCQ) blood levels are associated with a higher risk for thrombotic events, according to a study published online January 5 in Arthritis & Rheumatology.

Michelle Petri, MD, MPH, from the Johns Hopkins University School of Medicine in Baltimore, and colleagues examined HCQ blood monitoring in predicting thrombosis risk in a longitudinal SLE cohort. Mean HCQ blood levels were compared for patients with and without thrombosis; the association between rates of thrombosis and HCQ blood level was examined.

The researchers found that thrombosis occurred in 5.1% of the 739 patients with SLE. A lower mean HCQ blood level was seen in those with vs without thrombosis (720 ± 489 vs 935 ± 580). Thrombosis rates were reduced for every 200ng/mL increase in the most recent HCQ blood level and for mean HCQ blood level (rate ratios [95% confidence intervals], 0.87 [0.78 to 0.98; P =.025] and 0.87 [0.76 to 1.00; P =.056], respectively). Patients with mean HCQ blood levels >1068 vs <648ng/mL had a reduction in thrombotic events (rate ratio, 0.31; 95% confidence interval, 0.11 to 0.86; P =.024); the significant association persisted after adjustment for confounders (rate ratio, 0.34; 95% confidence interval, 0.12 to 0.94; P =.037).

“Empirical hydroxychloroquine dose reduction to less than 5mg/kg might reduce or eliminate the benefit of hydroxychloroquine in thrombosis prevention,” the authors write. “Routine clinical integration of hydroxychloroquine blood level measurement offers an opportunity for personalized drug dosing and risk management beyond rigid empirical dosing recommendations in patients with SLE.”

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