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Disclosures: The researchers report no relevant financial disclosures.
January 12, 2021
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Low hydroxychloroquine blood levels linked to thrombotic events in lupus

Source/Disclosures
Disclosures: The researchers report no relevant financial disclosures.
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A mean hydroxychloroquine blood level of more than 1,068 ng/mL is associated with a 69% reduction in thrombotic events, compared with blood levels of less than 648 ng/mL, among patients with systemic lupus erythematosus, according to data.

“Despite its widespread use since the 1950s, optimal dosing of HCQ in SLE is unknown,” Michelle Petri, MD, MPH, of Johns Hopkins University School of Medicine, and colleagues wrote in Arthritis & Rheumatology. “More recently, concern about retinopathy increased after a retrospective Kaiser-Permanente study. The retrospective Kaiser-Permanente study was the basis for the revised American Academy of Ophthalmology (AAO) guidance to limit hydroxychloroquine dosing to less than 5 mg/kg absolute body weight.”

“We need to move away from the weight-based dosing recommendations from ophthalmology to personalized medicine — meaning let’s adopt routine use of HCQ blood levels,” said Michelle Petri, MD, MPH. Source: Adobe Stock

“The Kaiser-Permanente study, however, was based on pharmacy dispensing records and not on the prescribed dose (which is higher due to partial adherence),” they added. “A study of 412 SLE patients recently suggested that empirical dose reduction following AAO guidelines was not associated with increased short-term risk of lupus related end-organ damage, but importantly did not look at therapeutic drugs levels or thromboembolic events.”

To analyze the utility of hydroxychloroquine blood monitoring in predicting thrombosis risk among patients with SLE, Petri and colleagues examined data from the Hopkins Lupus Cohort, a longitudinal study of SLE outcomes. In all, the researchers included 739 cohort participants with SLE and one or more hydroxychloroquine blood measurement. These measurements were serially quantified from EDTA whole blood via liquid chromatography‐tandem mass spectrometry.

Michelle Petri, MD, MPH
Michelle Petri

The researchers used t-tests to compare mean hydroxychloroquine blood levels recorded prior to thrombosis, or until the last visit, between participants with and without thrombosis. They then used pooled logistic regression to examine the link between thrombosis rates and hydroxychloroquine blood level.

According to the researchers, thrombosis occurred in 5.1% of included participants. Mean hydroxychloroquine blood levels were lower among participants who developed thrombosis, at 720 ± 489 ng/mL, compared with those without thrombosis, at 935 ± 580 ng/mL (P = .025). In addition, rates of thrombosis were reduced by 12% for every 200 ng/mL increase in the most recent hydroxychloroquine blood level (0.87; 95% CI, 0.78- 0.98), and by 13% for mean hydroxychloroquine blood level (rate ratio = 0.87; 95% CI, 0.76-1).

Participants with mean hydroxychloroquine blood levels of more than 1,068 ng/mL demonstrated a 69% reduction in thrombotic events, compared with those with a mean of less than 648 ng/mL (0.31; 95% CI, 0.11-0.86). This finding remained significant after adjusting for confounders (0.34; 95% CI, 0.12-0.94).

“We need to move away from the weight-based dosing recommendations from ophthalmology to personalized medicine — meaning let’s adopt routine use of HCQ blood levels,” Petri told Healio Rheumatology. “Low levels usually mean nonadherence. Using the Hopkins assay, the level needs to be around 1,000 to prevent thrombosis. The upper tertile on the Hopkins assay indicated increased risk of retinopathy. We shouldn’t be flying blind with HCQ dosing.”