In lupus, hydroxychloroquine blood levels matter more than dosage
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Rheumatologists treating patients with systemic lupus erythematosus should focus more on hydroxychloroquine blood levels than on prescribed dosage based on weight, according to a speaker at the 2020 Congress of Clinical Rheumatology-West.
“This is the part of the ophthalmology guidance that I don’t like,” Michelle A. Petri, MD, MPH, of the Johns Hopkins School of Medicine, told attendees at the virtual meeting. “I don’t like that 5 mg-per-kg rule because I don’t think we have one rule that fits all patients. I certainly never, ever, go above 400, and I reduce the dose in patients who have renal insufficiency or major liver problems, or who are elderly. However, I wanted to show you that what really matters is the blood level.”
To help make her case, Petri cited a 2019 study published in Arthritis & Rheumatology, in which she and colleagues demonstrated the usefulness of examining hydroxychloroquine blood levels when predicting retinopathy.
According to the researchers, their findings allow physicians to either decrease the dose or increase monitoring in patients with high hydroxychloroquine blood levels.
“We were also able to show that patients in the upper tertile of a blood level had greater risk for retinopathy,” Petri said. “So, please, do build in hydroxychloroquine blood levels into your practice, first of all to detect nonadherence — the patients who have a level of less than 500 [mg/dL] — but secondly to detect patients who are too high, those in the upper tertile, in whom you should be lowering the dose.”
In addition, Petri cautioned physicians to select blood levels, which reflect how much the patient received during the previous month, rather than plasma serum levels.
“There is no reason we should base our clinical decisions on a weight-based dosing scheme,” Petri said. “When you look at the slides, it becomes obvious: there is no relationship there.”
However, there are other benefits of examining hydroxychloroquine blood levels besides monitoring toxicity, according to Petri.
In a study presented at the American College of Rheumatology 2019 Annual Meeting, and published that same year in Arthritis & Rheumatology, she and colleagues demonstrated that hydroxychloroquine blood levels are inversely associated with the risk for any thrombosis, including venous thrombosis, among patients with SLE.
In that study, the researchers argued that reducing hydroxychloroquine doses, as suggested by the American Academy of Ophthalmologists, could reduce or eliminate the drug’s benefit in preventing thrombosis.
“Patients need a certain amount to get all the benefits,” Petri said. “Remembering that about 50% of our lupus patients will have antiphospholipid antibodies, I wanted to show you our more recent data that you really need to have a blood level of probably around 1,000 [mg/dL] to be able to prevent thrombosis. This is a new message: it’s not just toxicity that is predicted by hydroxychloroquine, but also benefit. So, it’s kind of like the story of Goldilocks. There is a nice sweet spot down the middle for hydroxychloroquine.”
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Petri M. Update on treatment of SLE. Presented at: Congress of Clinical Rheumatology-West annual symposium; October 8-11, 2020 (virtual meeting).
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